In a different environment than you, when I did troubleshooting of electronics I kept a journal of findings. Like ur white board but more permanent, every step taken with resulting findings were WRITTEN DOWN. This was quite useful whenever my mind started either getting over loaded or was going in circles. LOOKING at CONFUSING findings can result in an ah-ha moment. And is an absolute requirement if I ever question, "was my mind remembering correctly previous findings?" There are times when the process is rudimentary enough this isn't necessary and there are people who are greatly gifted at retaining extensive amounts of facts so writing is a waste of time. Guess I'd suggest to play it by ear and see if one finds ledgering to be beneficial.
Matt, since you cut the signal wire, you could measure voltage on the PCM side and the harness side. If voltage is present only on the PCM side, that would conclusively prove it is a PCM issue and not a wiring issue.
Spot on. I’ve measured voltage at the PCM output that was a different reading at the sensor connector due to internal damage in the harness. An overlay verifies the diagnosis.
Great video. Sometimes the computer tries to send a signal voltage to another sensor to try and calculate the variable resistance that it can not caculate. You saw and demonstrated good diagnosis for the students out there. Showi g and the affects what could be causing problems between the sensor or sensors and the computer. Great understanding of your expectations and explaining of desired goals. Great job!
I consider Schrodingers Box a mentor in this field. Scientific approach to mechanics never fails. If you live by the mantra, 'show your work', you should never replace a part without knowing it will fix the vehicle. Thank you.
For a pull up analog circuit is use a NPN Junction in the electronic. It has 3.3V on the Emitter and then reads it input voltage on the Collector and reads off the Base. You most likely have a blown transistor (Emitter and/or Collector is blown) circuit in the 3.3V.
BTW I'm one of the grateful subscribers to your website. I just finished the 7 videos on basic electricity and I finally get it! After 40 years of wrenching as a hobby and fearing anything electrical, I'm now looking forward to someone I know having an electrical problem so I can solve the case and fix it! On your recomendation I also bought the VDIAG power probe for a 100.00. There's a plethera of information on you website and anyone that hasn't joined either hasn't heard or is just plain stupid and doesn't want to learn!
Hahaha thanks man. Yes the the basic electrical series in my opinion is probably the best series I have ever done. I took extreme lengths to make sure the material can be learned.
"I forgot..I remember" lmao. Said by every dude who repairs something. I am going to sign up for your pay channel. You have a very good way of explaining things, even 11 yrs later.
Since 3.3V is typical supply voltage for low power ICs, that supports the hypothesis of that voltage coming from the ECM. That is, before obtaining full confirmation by cutting the wire.
Great instructional vid. I was about to say de-pin that yellow wire instead of cutting it. And after cutting the wire, shoulda totally broke the questionable ECM open to try to physically see with your eyeballs where an internal short could have occurred. Thanks Mr Schrodinger!!! .
I do have other videos where I dissect the PCM and show the damage on the circuit board. I didn’t do that in this video because cracking open a PCM is actually a difficult thing- they are sealed with some super roofing tar substance and the risk of destroying the PCM in the process is high. Given the car is completely drivable I didn’t want to risk making it dead in the water just for the video. PLUS apparently there is an 8-year warranty on PCM’s for emissions related issues. Cracking open a PCm would void that.
WOW MATT. AWESOME approach and thought process was thinking you will go to cut the wire but you went farther and took ur time to explain how the circuit works to ur viewers bravo brother and appreciate ur time for doing this thank you. cheeeeers
Well thank you. Yeah this has gotten a bit out of control lol- it’s probably past hobby at this point. In fact I am considering retiring from my real job and doing this full time and
Instead of cutting the wire, you could have removed the pin from PCM connector. That way the wire won't be cut and you don't have to invest time in repairing the wire
It is soooooo much faster repairing the wire than depinning and repinnin on that crowded connected. I spent 15 minutes trying to depin the wire but didn’t have the right remover. Why risk damaging the connection permanently?
Instead of cutting the wire.. you can pull apart that PCM connector and just de-pin your wire. Another way that may have worked-- you could have pulled the big PCM plug, and then just checked for the voltage on the pin itself on the PCM side; Granted, if the voltage was gone, that would be inconclusive because of all the other wires disconnected-- but if the voltage was still there -- that would be full confirmation. Also you could have done the same on the 2nd car to confirm. (granted, I know that checking those pins so close to each on PCM side is a little sketchy-- to not short pins out... so, gotta be careful).... The main other thing I would have been worried about (and maybe you did check off camera): Is that there could be corrosion inside that main PCM connector-- so I would have looked good and hard down inside there; Because if that's where the short was, it would still be there on your "cut the wire" test.............. Otherwise, great diag as always. Cheers
(Edit: forgot to mention, I love watching - this sort of trouble shooting should be mandatory in a lot of engineering classes ) Its difinitiveky possible the pcm is at fault, but I do think there is a risk, that the sings read as a faulty pcm may also be there on a good pcm. Sometimes multiplexed ADC’s leak signal from the previous position read by the multiplexer. It is high impedance, so no problem when there is a signal connected to the next position. But if it is floating, a signal may by detected (and typically correlated with the previous mux position). What if the potentiometer is disconnected? What is the resistance in the potentiometer? And by the way - if there was a leakage to a 5 v reference voltage and no other connections, you would measure 5 v on the wire touching the reference too (no current, no voltage drop, regardless of how small or bad the contact may be)
Good troubleshooting!👍. Usually within the PCM are many PN junctions as in diodes,transistors, and IC's, a breakdown of any silicone PN junction can happen ie heat/vibration and leak voltage in a direction that should be blocked by the PN junction creating your type of problem. The weak link are usually the IC's. Awesome video👍
100% correct. In fact in one of my pay channel videos I actually take apart a failed PCM and show exactly what you stated. You can actually see the damage on the circuit board!!!
There is probably a zener diode between the signal wire and 3.3V power inside the PCM to protect the MCU input from overvoltage. If the old sensor had a short between 12V and the signal this diode could have been overheated and blown. There are many repair shops who could fix this PCM.
@@Lou-eye I’m remembering 1981 when I first learned what a PN junction was and how solid state devices work. Maybe some UA-cam channel should create a series intended to teach the mechanic the basics of solid state devices and the buses of modern communications used in the auto industry. Wonder who could do that? 🤔 🤠🇺🇸
I wonder what is happening, I am a subscriber, but this is the first video to show up for me in ages. Am a big fan of your videos. Best regards from Western Australia.
@@SchrodingersBox will do, thank you for your answer. By the way, your analysis on this video was amazing. You're the best "non-mechanic" I have ever seen.
Great video though I am a little confused as my initial thought was that were would be a bias voltage coming from the ECU. What made you disregard that entirely? I have seen bias voltages ranging from all sorts of seemingly random numbers so I'm wondering if you know of a good way to determine whether its a bias voltage or a faulty ECU. Thanks!
Awesome job and interpretation ... I think based on the electronics that would be an internal shorted resistor...seen the fact that the pcm could not see the voltage drops across a potentiometer or in another world: the pcm reads only the voltage drop across that internal resistor based on the resistance changes at the sensor.
No. I’m literally not. I’m a scientist. That’s what I do for a living. That’s what my training is in. A hobby is not a profession. I edit my own videos but I am not a film editor. You made a comment but you aren’t an editorial writer.
@@SchrodingersBox You're wrong my guy.. lol.. You're a film producer/director/editor mechanic/Master Diagnostic Technician, who is paid to do science during business hours, for a day job.
Ok Finished video. Comment number two. Excellent diag. You're getting better. Remember you're doing videos with no scopes and autoengunuty scanner back then. Don't forget the tell me your thoughts on Topdon Scanner.
Thanks so much. Yeah I do remember actually saying at one point “I will never need a scope” hahahaa. Sheeesh. Honestly, the Topdon scanner works great but the interface is almost unbearable. Any scope I have used is fairly intuitive but not this one. The interface is clunky and challenging. But it absolutely works and gives beautiful resolution.
I agree. I tried but wasn’t able to and was more afraid of destroying the contact. That would have been way worse and less trustworthy repairing that mess than just soldering it together.
One extra step I could see being taken was to do a continuity check on the harness disconnected incase there was a wire short or a short in the connector itself.
@@SchrodingersBox it would have been a way to test without cutting. In my industry cutting for testing is a huge problem. Only non-destructive testing allowed.
Ah yes I see what you mean. Yes that is true, I probably should have done that. It’s a super pain working with that harness though. The wires are really hard to access and there isn’t much flexibility.
@@SchrodingersBox believe me I understand. Working in aviation i deal with smaller size and larger quantities of them. Access is always an issue. I do appreciate what you do and the content you provide. I am local to you if you ever need anything.
Hey Mattt, nice to see my mentor solving problems other proffesional can't! I was wondering why the TOPDON and not the Autel 906? I think you have the 906?
Thank you!! No reals reason for the TopDon - it’s just what I pulled off my shelf is all. I should have used the Autel (it’s an MS909) because I would have been able to pull more PIDs on screen at once when doing the signal ground out test.
23:27 "Well what's the point in that? How is that in any way useful whatsoever?...Well I forgot." 🤣 Holy crap that's hilarious, and reminded me of myself thinking ahead of what I'm currently saying.
It’s not just the Topdon all of the scan tools including the GDS2 categorizes the data streams the same way. 15 psi is close to what we see as baro down here in the flat lands of Louisiana. Baro and map should be the same with the engine not running. It’s nice to see techs that are aware of substituted values. Can’t tell you how many times I see inexperienced techs go down a rabbit hole due to substituted values 😂
Yes 15PSI would actually be a little below sea level- which Louisiana is. There is no way I should see that in Denver Colorado lol. That’s how I knew it was off.
Sensor ground comes from the PCM and then branches off to each individual sensor. If there is high resistance between the branching-off point and the sensor, that would cause the voltage reading of that sensor to be elevated without affecting other sensors. For example, if the barometric pressure sensor has a bad pin fitment at its sensor ground terminal (causing high resistance) that could cause an elevated voltage reading on the signal wire (without affecting other sensors). It's possible someone stuffed a T-pin into a female terminal and spread open the terminal. If the spread open terminal is on the harness side, then the problem will still be there even if you replace the sensor. You can't detect a bad pin fitment issue by backprobing. The only way to detect a bad pin fitment issue is to use a terminal test kit and slide a test male terminal into the suspect female terminal and see if there is proper drag.
Only other option could’ve been to de pin that wire from the pcm harness. Although depending on how annoying the connector is it might just have been easier to cut the wire and repair it lol. I’ve been in the field about 15 years and I also have probably only ever called less than 10 PCMs. Funny enough though one of them just happened last week lol. 2014 4Runner came in crank no start, customer said it just shut off on the highway. Quickly discovered that I had no comm with the PCM. I checked all my powers and grounds, and verified communication lines with the scope. And then I sat there for probably 2 hours combing through the wiring diagram and theory and operation because I’ve never seen this on a Toyota and it was really bothering me to make the call. But eventually I had no other option and made the call. Cool enough though the new PCM didn’t need to be programmed and all I had to do was program the VIN which I could do with my scanner and it fired right up and good to go. I also had to call a BCM on a ford last week lol, no right rear turn signal, that was a super easy diagnostic though, BCM just simply wasn’t sending a signal out for the right rear.
Had the same code on my 2011 Impala, I traced it down to a very tight wiring harness to the MAF, where wires were stretched and shorting. Cut the wires and soldered, oh and pulled some length for the harness
Yeah that’s what is fun about this. There are sooooo many ways to approach this. I am kind of disappointed the PCM was the issue not so much because it means I can’t do an instant fix- but it this was from a short to power on another wire, it would have been amazing to catch it on the scantool PIDs when grounding the signal wire out.
you need to send a 0.050 amp 5 volt signal on that wire....it the 5 volts drops you have something pulling the signal down...the power probe hook has that ability to do that yet, they do not make that anymore...power probe has a 5 volt generator to add to a power probe, it supplies 0.100 amp 5 volt signal and it will drop if something is pulling the signal down
How many miles are on this? PCM warranty should be 8yr/80,000miles. BTW. A common GM strategy is for a signal wire to have an internal resistor connected to the 5v. That is done for self diagnostics. According to SI this Baro sensor circuit should go high (5v) when disconnected. Check your email.
I would absolutely love that!! Paul and I actually talk on the phone a couple times a year and I have met him in person several times. Even watched him play hockey (he’s really good). Hopefully I’ll be able to line up a video with him someday.
Matt I was wondering why you are claiming the sensor should have no voltage on the signal wire with the sensor unplugged. The pico scope has much less internal impedance (2k), and will pull the 5volt pull up voltage low just slightly,which is why it was 4 volts. A voltmeter with 10meg ohm would have showed around 4.85vdc In service information it states very clearly the signal wire is tied resistively to 5volts. The wiring diagram also shows a pull up resistor. Why didn’t you pull a wiring diagram at all. Most late model engine management systems will almost always use a pull up resistor on the ckt for diagnostics I don’t know how you showed what you showed in the other vehicle. Sorry to say otherwise I mean no disrespect. I truly appreciate what you do.
That was really in depth, could be pull down circuit in some cases, think some pressure signal wires has that. Did you saw some change on baro pressure pid when you pulled signal wire to ground.
@@SchrodingersBox thank you when you unplugged connector voltage was going down so that was proof that is pull up circuit. Did you know previous circuit design.
Thanks for asking. Once I rebuilt the T/A I traded it in for a hellcat. The T/A is just too old to handle the extreme horsepower I put on it and I didn’t want to keep chasing these catastrophic failures every couple of years.
I don’t follow- the PCM is still going to measure voltage before the resistor right? I would have to put that resistor in front of the PCM voltage detector.
@@SchrodingersBox The wire going into the PCM likely goes through a resistor to ground inside the PCM's housing - true. However the sensing device inside the PCM (likely the base of a FET or transistor) is connected to the same wire that comes into the PCM (before the aforementioned resistor to ground). If you put a resistor outside the PCM to ground it will affect the wire inside the PCM as well. The theory is that if there a problem with the resistor inside the PCM (cold solder joint perhaps) the resistor you'd add outside the PCM will do the job of the internal resistor. My background is physics and electrical engineering, but I grew up in a garage. I sometimes don't explain enough when commenting. It's a longshot attempt, but a $5 10k ohm variable resistor (potentiometer) will allow you to test the theory. Wish I could draw you a picture. :)
@@frederiknielsen4987 It may be the PCM's internal resistor (if they use that tech) is a little fried and has changed its value. If he was to insert a variable resistor to ground he might be able to adjust out the offset error.
I really learn a lot from your videos, thanks for taking the time to make them. With the wire being a 5v reference, would measuring resistance on the wire be detailed enough to determine if it is damaged?
That would be a good test however this is not a 5V reference wire. It is a signal wire. The issue is not resistance. It’s that it has a voltage on it. Also I did indirectly test resistance on it… when I grounded the signal out it did go to 0V. If the wire had resistance it wouldn’t have gone to 0V.
Matt, you are the BEST. I love you man. Your brilliant deductive approach, humility, sense of humor, and desire to TEACH as you go make you stand way above the crowd. All that and good looks too, lol. "Let's ground out this signal... how is that in any way useful whatever? Uh well, I forgot, NO I remember... " 😂 23:22
It's a 2017 Chevy. Eric would run down to Wilmer's and get a PCM. You believe PCMs rarely fail, so a junk yard PCM is a reasonable solution for a 2017 Chevy.
DIYer here, so don't listen to me too much, but one thing we could have done is to measure resistance, on the connector at the harness side, while unplugged from the PCM, between the signal wire and the rest, right? To check if the signal wire had good isolation from all other wires (obviously it was going to give lower resistance with the 5V reference and the ground of the barometric sensor). But if there was some sort of short circuit with another wire with voltage, it would have appeared as lower resistance I think...
@@SchrodingersBox No, not when you grounded it. Probably I haven't done a good job explaining myself. What I mean is we could do the same thing that electricians do to the electric installation of a house. They switch off the circuits and check the impedance (resistance in the case of cars) of the line cable with the earth and the neutral with earth. If there is a short circuit or some sort of connection between the cables, instead of infinite or lots of Mohm, you're going to see some KOhms or even ohms. So if you disconnect the connector from the PCM, the resistance between the cables and the barometric signal cable should be close to infinite (with a few exceptions, like the 5V reference for the sensor, etc.). And this checks are done with no voltage applied to anything, we're just checking for some sort of continuity/resistance between cables that should have none, since they should be isolated from each other.
I was screaming bias voltage at my screen the whole time until you showed the control car with a zero volt bias with the connector unplugged (or at least you proved that 0psi does not correspond to 3.3V). I would also check grounds at the PCM as there could technically be a signal ground feeding 3.3V to the computer instead of 0V, but I don't see how that would affect just the baro sensor.
@@SchrodingersBox Bias voltage can be any voltage you want (there are videos by Ivan, Paul and Eric O with biases of 2V, 3V and many other voltages on various sensor circuits. It can be done with a voltage divider inside the module), however the impedance associated with this voltage is orders of magnitude higher than what the sensor itself produces, so the sensor should still be capable of pulling this bias down to 0 V or up to 5V. In your video, you show clear evidence that the PCM is actually supposed to have a 0V bias, rather than 3V, hence the PCM is bad.
I did. There was no voltage on it with connector unplugged at PCM. But more importantly we see the voltage drop to zero when wire was cut. This means there was definitely voltage at the pin on the PCM. You usually can’t look for voltage on the pin when the connector is unplugged because you lose the power feed to the PCM.
@@SchrodingersBox I agree with you: "UNLESS the short was right there inside the PCM connector-- like with some corrosion shorting across the pins. But I assume you looked closely down inside the PCM connectors once you pulled it apart.
Yes I did try that but it wasn’t being very agreeable and I was more concerned about destroying the contact. Much safer and faster to just cut and solder.
Im not following what that will do exactly- how does that apply for voltage on the wire? I would certainly do that for a suspected high resistance but this is a voltage contamination issue.
Couldn’t you disconnect the pcm connector and do continuity checks with the meter between the yellow wire and all the wires on that particular harness at the pcm? That way you can isolate which wire is shorting together.. Also, what if that voltage is a bias voltage from the pcm used as a diagnostic purpose
No need to we have overwhelming evidence from the ground-out test on every PID that this is not the result of it shorting to a wire externally. It is so much faster to just isolate that signal wire than to check hundreds of pins.
Could the Terrains pcm be close enough to swap for testing to avoid wire cut... then be placed back in terrain without needing some reprogramming...secuirity key etc... Thanks
How can there a bent pin and be both power and signal return though? Not possible unless each pin is aligned in its slot. Plus all other PCM PIDs were 100% normal and no other codes or issues.
@@SchrodingersBox Thanks. I'll have to look at the video again to see what I missed.... not that I know what happens when you introduce an additional voltage at that point (i.e. at the PCM plug from a bent pin). A series/parallel nightmare. I was thinking perhaps that the normal signal voltage might have been, say, 0.7 volts and, with an additional voltage of 3.3 volts from a foreign source, the signal might have been boosted to 4 volts. Anyway, as you say, there were no other issues.
The barometric pressure read 15psi you said that's the problem but the scan tool range said 9-16psi is standard ?🤔 I have a top don scanner so I was thinking if the numbers are in that range it good and if it's not it would be red and yall know it's a problem?
Am I crazy/wrong? Or could you unplug the connector at the pcm, then check for continuity with a DMM between that baro signal wire and every other wire in that plug ?
Yes I could do that but no need to. So much quicker to just cut the wire and confirm voltage went to zero. There are maybe 200 wires in that PCM- no way I am probing each one lol.
Did a PCM fix it? Cutting the wire shouldn’t loose voltage if voltage is coming from PCM?? If voltage is lost cutting wire, voltage came from harness? PCM reads the voltage??
You have it backwards. Cutting the wire isolated the signal circuit. If voltage is still there then the voltage source is not from the PCM. But since cutting the wire dropped the voltage, the voltage had to only be from the PCM. There is no other voltage source because it went to zero.
Choosing to cut it out and jump it as the last step is probably the safest choice you can make. I don't think you touched on bias voltage? If that circuit used bias voltage to verify the integrity of the circuit you would be potentially throwing a PCM at it for nothing! Most people forget that bias voltage isn't constant... it is usually momentarily or when something is unplugged / powered off. Bias voltage is actually how the PCM runs comprehensive monitors to determine if their is a circuit related fault!
There are only two systems used- neither have bias voltage. Either you will have zero V on signal when unplugged or 5V with it unplugged. But in no system for the GM is there 3.3V possible. Either way it’s an internal PCM fault.
@SchrodingersBox bias voltage isn't always in half volt increments. More complicated systems integrate bias voltage on circuits connecting two seperate modules. 19+ ram cummins is a good example of bias voltage that looks like stray voltage. It has bias voltage for both the low and high side drivers that actuate the starter relay. There is no constant ground or power. The PCM supplies the high side and the BCM supplys the low side. If you pull the starter relay out you will get odd readings for bias voltage... but there isn't anything wrong with it. Bias voltage across two modules connected by a starter relay inherintely requires an odd bias voltage because otherwise the starter might sporatically engage when it shouldn't... just an example of bias voltage that might not make sense when you first encounter it...
Correct. I should have said only two systems used on GM of this era specifically. Absolutely some other systems have bias voltage and in fact I have videos showing this on those models. This model doesn’t have it though.
I did try delinking it but was not having success and was more likely to destroy the contact. Cutting was safer. Fixing a wire is easy- solder and heat shrink is a permanent repair.
Often times it’s best to have an extraction tool designed specifically for the connector. Save that, the cut/solder/shrink method is perfect and relatively speedy. Enjoy your content! 🤠🇺🇸
@@thecode3fc I had a recent connector I tried to remove a pin on and I spent WAY too long trying to do it and I'm not sure if the connector is now bad. Where would I find tools to do this? I resorted to a small pick, but it was still too big.
There are depinning kits which basically have really thin tubes that you fit over the pin and it depresses the retention tabs. Kind of like a fuel like disconnect tool. But you have to have exactly the right size or you can damage the pin.
How can there not be power and ground to the PCM? Every single parameter works and the issue is voltage on a signal wire that shows variance. Can’t happen without power and ground on the PCM.
@@SchrodingersBox There are usually multiple power wires and multiple ground wires that feed different parts of the computer. If one power wire has low voltage or bad ground wire strange things can happen inside the computer. Checking those pins easy enough and a best practice kind of thing.
Yes true but we can see clearly this is not a power or ground problem just from the data. It’s not a ground problem because the voltage dropped to zero when I provided external ground- that can’t happen with a good ground. And we know there isn’t a power problem because first, all 5V references were powered and second, there was confirmed 5v ref to this specific circuit. Checking powers and grounds on the PCm would be a waste of time because we know they are good.
Yes many people asked about this. I did try depinning it but I didn’t have the right tool so I was afraid I was more likely to damage the contact. Cutting it was far safer.
Lots of people asked that- good though but no. Unplugged you will have only two systems on here- on with no voltage or one with 5V reference that shows up past a resistor. 3.3 is not possible in either.
Not on a signal wire from a potentiometer. From a Hall effect or inductive maybe, not not a potentiometer. Also we saw there is no voltage present from the same system on the GMC vehicle.
VERY good question and absolutely a major concern. As I mentioned many many times, just throwing a PCM in without electrical checks first will likely cause the same issue in the new PCM. Great point, man!!
I'm at the 39.40 minute mark where you are considering cutting the yellow wire at the PCM. Granted, I'm not a mechanic but an electrician and at this point, I would ohm the yellow wires against all the other wires in the connector because I would assume that none of them should have continuity at all with any of the others. if it does, that would be the wire you would want to chase down to see if it's touching your yellow wire. If it doesn't, I would then turn around and test the pin on the ECU with the key on to see if the voltage is coming from the ECU, if it is, then I would assume it's a bad ECU...There's got to be a better way than cutting the yellow wire, right? Aight, lets see how this ends. *unpause*
There is no way I am ohming 300 wires as opposed to just simply cutting one and confirming the issue and resoldering it. If an electrician is going to literally ohm 300 wires instead of a simple test and permanent repair I would argue I am a way better electrician!!!
hahahahaha. well I think that would be funny if a cave man took an Uber up to me and then was only mesmerized after seeing me do this diagnosis hahaha!!!!
Weird how a PCM would go bad, just like that. Maybe a jump-start gone wrong? Would invest in a de-pinning kit though. Or maybe some US-based subscriber can gift you one.
@@SchrodingersBox I just started the video, so no evidence just my guess. If green crusties are present, couldnt that introduce voltage from a different wire?
No it would reduce resistance. Not sure I see why guessing without evidence would be in any way fun- seems way more fun to gather the evidence and then formulate a conclusion you know must be correct doesn’t it? Well for me it does. Even if I guess correctly it’s still wrong.
Could I pay you to help me troubleshoot ? I have taken data logs and numerous testing watched all your videos multiple times and I just can't figure it out . Thanks
@@SchrodingersBox lol I wouldn't dare to with an individual of your expertise . 04 lexus rx330 @ idle LTFT 10% or more increases until I hit around 4000 rpm then they drop to only 4% but constantly dumping fuel never (-)
. I still don’t know what the issue is with the car. Is it a check engine light? Is it running lean? Is it lacking power? I need something to start with here.
@@SchrodingersBox car jerks from 2500 to 4000 rpm then picks up . Had quite a few codes fixed vacuum leaks due to old cracked hoses . Original codes were p0300 and p0430
Yes many people said that. I did try and wasn’t able to and was more afraid of destroying the contacts. Soldering a wire is easier than replacing the pin if I destroy it.
32:49... I really liked you grounding your suspect signal and then reading selected pids for change but have an alternate thought. Might you first clear all current error codes and with signal again grounded see if any NEW codes popup. And/or does grounding signal prevent the code of this troubleshooting?
Thanks! I see your thinking but what would happen is I would only get new codes popping up if I changed the PIDs drastically with the ground out of the signal. But I would see the PIDs change so the new codes wouldn’t be relevant anyway. After doing all this the only code was still the P2227 but also a P2229 (I think it was) for a low baro circuit voltage due to grounding it out.
18:18 No Monday morning quarterback here. Personally I would stop now and go directly to the wiring harness, knowing that there is constant voltage. Visual inspection should lead to your problem source, I'd bet. That's my honest 2 cents. I will watch the rest of the video now to learn what happens.
Yeah we had the same thought but I thoroughly inspected the harness and it was clear the contaminating voltage was definitely from the PCM and not an adjacent wire.
Ummm learn how to follow a test plan, this is a basic 3 wire set up and at most would require 10 minutes of diag. You missed one big step, discount the PCM connector and inspect for moisture intrusion. Wasted 45 minutes of my live watching a chop shop diag !!!!!!
Hahahahahaha well you obviously have no diagnostic skills at all. How would have determined in 10 minutes that this wasn’t a power feed crossover in the harness. I’m waiting for your explanation you idiot.
In a different environment than you, when I did troubleshooting of electronics I kept a journal of findings. Like ur white board but more permanent, every step taken with resulting findings were WRITTEN DOWN. This was quite useful whenever my mind started either getting over loaded or was going in circles. LOOKING at CONFUSING findings can result in an ah-ha moment. And is an absolute requirement if I ever question, "was my mind remembering correctly previous findings?"
There are times when the process is rudimentary enough this isn't necessary and there are people who are greatly gifted at retaining extensive amounts of facts so writing is a waste of time. Guess I'd suggest to play it by ear and see if one finds ledgering to be beneficial.
Matt, since you cut the signal wire, you could measure voltage on the PCM side and the harness side. If voltage is present only on the PCM side, that would conclusively prove it is a PCM issue and not a wiring issue.
I was thinking the same thing. That would be 100% proof.
Yeah it's easy for us to say this when everything was procedurally laid out for us ahead of time.
There is no need to do that. We know the voltage was from PCM side. Otherwise how can the voltage drop to zero?
Spot on. I’ve measured voltage at the PCM output that was a different reading at the sensor connector due to internal damage in the harness. An overlay verifies the diagnosis.
@@SchrodingersBox yes, you are correct. I missed that check.
Great video. Sometimes the computer tries to send a signal voltage to another sensor to try and calculate the variable resistance that it can not caculate.
You saw and demonstrated good diagnosis for the students out there. Showi g and the affects what could be causing problems between the sensor or sensors and the computer.
Great understanding of your expectations and explaining of desired goals.
Great job!
I consider Schrodingers Box a mentor in this field. Scientific approach to mechanics never fails.
If you live by the mantra, 'show your work', you should never replace a part without knowing it will fix the vehicle.
Thank you.
Love your philosophy!!
For a pull up analog circuit is use a NPN Junction in the electronic. It has 3.3V on the Emitter and then reads it input voltage on the Collector and reads off the Base. You most likely have a blown transistor (Emitter and/or Collector is blown) circuit in the 3.3V.
BTW I'm one of the grateful subscribers to your website. I just finished the 7 videos on basic electricity and I finally get it! After 40 years of wrenching as a hobby and fearing anything electrical, I'm now looking forward to someone I know having an electrical problem so I can solve the case and fix it! On your recomendation I also bought the VDIAG power probe for a 100.00.
There's a plethera of information on you website and anyone that hasn't joined either hasn't heard or is just plain stupid and doesn't want to learn!
Hahaha thanks man. Yes the the basic electrical series in my opinion is probably the best series I have ever done. I took extreme lengths to make sure the material can be learned.
Thanks for all the quality content. South main Auto and yourself are top notch.
Honored to be considered in such company, thanks!!
"I forgot..I remember" lmao. Said by every dude who repairs something. I am going to sign up for your pay channel. You have a very good way of explaining things, even 11 yrs later.
I really appreciate that!!! You will
Love it. It’s my very best videos.
“I don’t know, I’m not a mechanic”
You’re more thorough and have better skills than 75% of technicians that I’ve worked with over the years.
Since 3.3V is typical supply voltage for low power ICs, that supports the hypothesis of that voltage coming from the ECM. That is, before obtaining full confirmation by cutting the wire.
Great instructional vid. I was about to say de-pin that yellow wire instead of cutting it. And after cutting the wire, shoulda totally broke the questionable ECM open to try to physically see with your eyeballs where an internal short could have occurred. Thanks Mr Schrodinger!!! .
I do have other videos where I dissect the PCM and show the damage on the circuit board. I didn’t do that in this video because cracking open a PCM is actually a difficult thing- they are sealed with some super roofing tar substance and the risk of destroying the PCM in the process is high. Given the car is completely drivable I didn’t want to risk making it dead in the water just for the video. PLUS apparently there is an 8-year warranty on PCM’s for emissions related issues. Cracking open a PCm would void that.
WOW MATT. AWESOME approach and thought process was thinking you will go to cut the wire but you went farther and took ur time to explain how the circuit works to ur viewers bravo brother and appreciate ur time for doing this thank you. cheeeeers
Thanks for sharing, always learn something when I watch your videos
I always learn something when I make them too!!
As a hobbyist, you are head and shoulders above most "mechanics" with your diagnostic abilities.
Well thank you. Yeah this has gotten a bit out of control lol- it’s probably past hobby at this point. In fact I am considering retiring from my real job and doing this full time and
Instead of cutting the wire, you could have removed the pin from PCM connector. That way the wire won't be cut and you don't have to invest time in repairing the wire
It is soooooo much faster repairing the wire than depinning and repinnin on that crowded connected. I spent 15 minutes trying to depin the wire but didn’t have the right remover.
Why risk damaging the connection permanently?
Instead of cutting the wire.. you can pull apart that PCM connector and just de-pin your wire. Another way that may have worked-- you could have pulled the big PCM plug, and then just checked for the voltage on the pin itself on the PCM side; Granted, if the voltage was gone, that would be inconclusive because of all the other wires disconnected-- but if the voltage was still there -- that would be full confirmation. Also you could have done the same on the 2nd car to confirm. (granted, I know that checking those pins so close to each on PCM side is a little sketchy-- to not short pins out... so, gotta be careful).... The main other thing I would have been worried about (and maybe you did check off camera): Is that there could be corrosion inside that main PCM connector-- so I would have looked good and hard down inside there; Because if that's where the short was, it would still be there on your "cut the wire" test.............. Otherwise, great diag as always. Cheers
(Edit: forgot to mention, I love watching - this sort of trouble shooting should be mandatory in a lot of engineering classes ) Its difinitiveky possible the pcm is at fault, but I do think there is a risk, that the sings read as a faulty pcm may also be there on a good pcm. Sometimes multiplexed ADC’s leak signal from the previous position read by the multiplexer. It is high impedance, so no problem when there is a signal connected to the next position. But if it is floating, a signal may by detected (and typically correlated with the previous mux position). What if the potentiometer is disconnected? What is the resistance in the potentiometer? And by the way - if there was a leakage to a 5 v reference voltage and no other connections, you would measure 5 v on the wire touching the reference too (no current, no voltage drop, regardless of how small or bad the contact may be)
Good troubleshooting!👍. Usually within the PCM are many PN junctions as in diodes,transistors, and IC's, a breakdown of any silicone PN junction can happen ie heat/vibration and leak voltage in a direction that should be blocked by the PN junction creating your type of problem. The weak link are usually the IC's. Awesome video👍
100% correct. In fact in one of my pay channel videos I actually take apart a failed PCM and show exactly what you stated. You can actually see the damage on the circuit board!!!
There is probably a zener diode between the signal wire and 3.3V power inside the PCM to protect the MCU input from overvoltage. If the old sensor had a short between 12V and the signal this diode could have been overheated and blown.
There are many repair shops who could fix this PCM.
@@Lou-eye I’m remembering 1981 when I first learned what a PN junction was and how solid state devices work. Maybe some UA-cam channel should create a series intended to teach the mechanic the basics of solid state devices and the buses of modern communications used in the auto industry. Wonder who could do that? 🤔 🤠🇺🇸
Yes great point and in fact I recommended they send the PCM in to Flagship One which does exactly that!!!
I wonder what is happening, I am a subscriber, but this is the first video to show up for me in ages. Am a big fan of your videos. Best regards from Western Australia.
Hmmm I am not sure what to say about that?? Maybe unsubscribe and re-subscribe and see if that fixes it?
@@SchrodingersBox will do, thank you for your answer. By the way, your analysis on this video was amazing. You're the best "non-mechanic" I have ever seen.
Nice job Matt! Now all you need to do is to start programming! Fly me out and I'll bring my equipment along. Gm's I am familiar with.
Would totally love to do that!!!
Great video though I am a little confused as my initial thought was that were would be a bias voltage coming from the ECU. What made you disregard that entirely? I have seen bias voltages ranging from all sorts of seemingly random numbers so I'm wondering if you know of a good way to determine whether its a bias voltage or a faulty ECU. Thanks!
Awesome job and interpretation ...
I think based on the electronics that would be an internal shorted resistor...seen the fact that the pcm could not see the voltage drops across a potentiometer or in another world: the pcm reads only the voltage drop across that internal resistor based on the resistance changes at the sensor.
That’s exactly what I believe it is too!!
"Im not a mechanic." Just because being a mechanic is not your chosen profession, doesnt mean youre not a mechanic. Youre a mechanic, dude.
No. I’m literally not. I’m a scientist. That’s what I do for a living. That’s what my training is in. A hobby is not a profession. I edit my own videos but I am not a film editor. You made a comment but you aren’t an editorial writer.
@@SchrodingersBox You're wrong my guy.. lol.. You're a film producer/director/editor mechanic/Master Diagnostic Technician, who is paid to do science during business hours, for a day job.
Ok
Finished video. Comment number two. Excellent diag. You're getting better. Remember you're doing videos with no scopes and autoengunuty scanner back then. Don't forget the tell me your thoughts on Topdon Scanner.
Thanks so much. Yeah I do remember actually saying at one point “I will never need a scope” hahahaa. Sheeesh.
Honestly, the Topdon scanner works great but the interface is almost unbearable. Any scope I have used is fairly intuitive but not this one. The interface is clunky and challenging. But it absolutely works and gives beautiful resolution.
The better way to isolate the wire in question is to de pin the wire at the connector
I agree. I tried but wasn’t able to and was more afraid of destroying the contact. That would have been way worse and less trustworthy repairing that mess than just soldering it together.
@@SchrodingersBox You are right
@@SchrodingersBox Guess that's an excuse for a de-pin kit :) Because I was going to suggest the same.
One extra step I could see being taken was to do a continuity check on the harness disconnected incase there was a wire short or a short in the connector itself.
There was no need. When the wire was cut the voltage went to read zero.
@@SchrodingersBox it would have been a way to test without cutting. In my industry cutting for testing is a huge problem. Only non-destructive testing allowed.
Ah yes I see what you mean. Yes that is true, I probably should have done that. It’s a super pain working with that harness though. The wires are really hard to access and there isn’t much flexibility.
@@SchrodingersBox believe me I understand. Working in aviation i deal with smaller size and larger quantities of them. Access is always an issue. I do appreciate what you do and the content you provide. I am local to you if you ever need anything.
Oh good to know!! Whereabouts are you? I’m in Parker.
Today I learned that PWM is considered digital.
Yes correct! PWM is digital due to the “on/off”, vs analog which is always on but with varying degrees of voltage.
Hey Mattt, nice to see my mentor solving problems other proffesional can't! I was wondering why the TOPDON and not the Autel 906? I think you have the 906?
Thank you!! No reals reason for the TopDon - it’s just what I pulled off my shelf is all. I should have used the Autel (it’s an MS909) because I would have been able to pull more PIDs on screen at once when doing the signal ground out test.
I thought this video was more educational than entertaining.😃
Cheers.
Watch some of his other videos. Matt is hilarious. I love his cerebral humor.
Oh thanks man!! Cat vs Trolls videos??
@@SchrodingersBox Entertaining for sure.
Great content as always. Thanks a lot for sharing knowledge.
23:27 "Well what's the point in that? How is that in any way useful whatsoever?...Well I forgot." 🤣
Holy crap that's hilarious, and reminded me of myself thinking ahead of what I'm currently saying.
It’s not just the Topdon all of the scan tools including the GDS2 categorizes the data streams the same way. 15 psi is close to what we see as baro down here in the flat lands of Louisiana. Baro and map should be the same with the engine not running. It’s nice to see techs that are aware of substituted values. Can’t tell you how many times I see inexperienced techs go down a rabbit hole due to substituted values 😂
Yes 15PSI would actually be a little below sea level- which Louisiana is. There is no way I should see that in Denver Colorado lol. That’s how I knew it was off.
Very good diag. First time to see your channel. Very hands on.
Welcome aboard!!!
Sensor ground comes from the PCM and then branches off to each individual sensor. If there is high resistance between the branching-off point and the sensor, that would cause the voltage reading of that sensor to be elevated without affecting other sensors. For example, if the barometric pressure sensor has a bad pin fitment at its sensor ground terminal (causing high resistance) that could cause an elevated voltage reading on the signal wire (without affecting other sensors). It's possible someone stuffed a T-pin into a female terminal and spread open the terminal. If the spread open terminal is on the harness side, then the problem will still be there even if you replace the sensor. You can't detect a bad pin fitment issue by backprobing. The only way to detect a bad pin fitment issue is to use a terminal test kit and slide a test male terminal into the suspect female terminal and see if there is proper drag.
Thank you for sharing this with us, Matt! God bless.
My pleasure!
Only other option could’ve been to de pin that wire from the pcm harness. Although depending on how annoying the connector is it might just have been easier to cut the wire and repair it lol. I’ve been in the field about 15 years and I also have probably only ever called less than 10 PCMs. Funny enough though one of them just happened last week lol. 2014 4Runner came in crank no start, customer said it just shut off on the highway. Quickly discovered that I had no comm with the PCM. I checked all my powers and grounds, and verified communication lines with the scope. And then I sat there for probably 2 hours combing through the wiring diagram and theory and operation because I’ve never seen this on a Toyota and it was really bothering me to make the call. But eventually I had no other option and made the call. Cool enough though the new PCM didn’t need to be programmed and all I had to do was program the VIN which I could do with my scanner and it fired right up and good to go. I also had to call a BCM on a ford last week lol, no right rear turn signal, that was a super easy diagnostic though, BCM just simply wasn’t sending a signal out for the right rear.
Yes off camera I did try depinning it but it wasn’t working and I was more likely to destroy the contact. So much easier to cut and solder it.
Had the same code on my 2011 Impala, I traced it down to a very tight wiring harness to the MAF, where wires were stretched and shorting. Cut the wires and soldered, oh and pulled some length for the harness
What was your voltage on the signal showing?
My Goodness.....all the advice here makes my head spin already.....
Yeah that’s what is fun about this. There are sooooo many ways to approach this. I am kind of disappointed the PCM was the issue not so much because it means I can’t do an instant fix- but it this was from a short to power on another wire, it would have been amazing to catch it on the scantool PIDs when grounding the signal wire out.
good video
you need to send a 0.050 amp 5 volt signal on that wire....it the 5 volts drops you have something pulling the signal down...the power probe hook has that ability to do that yet, they do not make that anymore...power probe has a 5 volt generator to add to a power probe, it supplies 0.100 amp 5 volt signal and it will drop if something is pulling the signal down
Ok, let me subscribe to your website 👍🏽
Please do!
How many miles are on this? PCM warranty should be 8yr/80,000miles. BTW. A common GM strategy is for a signal wire to have an internal resistor connected to the 5v. That is done for self diagnostics. According to SI this Baro sensor circuit should go high (5v) when disconnected. Check your email.
Thanks John!!! Yes I very much appreciate the the email!!
Matt, would love to see a collaboration with you and Scanner Danner!
I would absolutely love that!! Paul and I actually talk on the phone a couple times a year and I have met him in person several times. Even watched him play hockey (he’s really good).
Hopefully I’ll be able to line up a video with him someday.
Matt I was wondering why you are claiming the sensor should have no voltage on the signal wire with the sensor unplugged.
The pico scope has much less internal impedance (2k), and will pull the 5volt pull up voltage low just slightly,which is why it was 4 volts. A voltmeter with 10meg ohm would have showed around 4.85vdc
In service information it states very clearly the signal wire is tied resistively to 5volts.
The wiring diagram also shows a pull up resistor.
Why didn’t you pull a wiring diagram at all.
Most late model engine management systems will almost always use a pull up resistor on the ckt for diagnostics
I don’t know how you showed what you showed in the other vehicle. Sorry to say otherwise
I mean no disrespect.
I truly appreciate what you do.
That was really in depth, could be pull down circuit in some cases, think some pressure signal wires has that. Did you saw some change on baro pressure pid when you pulled signal wire to ground.
Yes great point- I missed showing it in the edits but I remember the baro showed zero on pull down of signal
@@SchrodingersBox thank you when you unplugged connector voltage was going down so that was proof that is pull up circuit. Did you know previous circuit design.
Great video, one question, what happened to your T/A? I noticed the switch during your polishing videos, so did I miss something?
Thanks for asking. Once I rebuilt the T/A I traded it in for a hellcat. The T/A is just too old to handle the extreme horsepower I put on it and I didn’t want to keep chasing these catastrophic failures every couple of years.
@@SchrodingersBox yep, I understand that, good luck with your new ride.
Maybe it just needs a pull-down resistor. Agreed the PCM is malfunctioning, but a 15 cent resistor might still work.
I don’t follow- the PCM is still going to measure voltage before the resistor right? I would have to put that resistor in front of the PCM voltage detector.
Yes, because it’s floating (although remarkable stable)
@@SchrodingersBox The wire going into the PCM likely goes through a resistor to ground inside the PCM's housing - true. However the sensing device inside the PCM (likely the base of a FET or transistor) is connected to the same wire that comes into the PCM (before the aforementioned resistor to ground). If you put a resistor outside the PCM to ground it will affect the wire inside the PCM as well. The theory is that if there a problem with the resistor inside the PCM (cold solder joint perhaps) the resistor you'd add outside the PCM will do the job of the internal resistor. My background is physics and electrical engineering, but I grew up in a garage. I sometimes don't explain enough when commenting. It's a longshot attempt, but a $5 10k ohm variable resistor (potentiometer) will allow you to test the theory. Wish I could draw you a picture. :)
@@frederiknielsen4987 It may be the PCM's internal resistor (if they use that tech) is a little fried and has changed its value. If he was to insert a variable resistor to ground he might be able to adjust out the offset error.
I follow what you are saying and I didn’t think about this at the time but I agree you are correct b
Hi Schro! Long time no view!
I’ve been here!! welcome back!
I really learn a lot from your videos, thanks for taking the time to make them.
With the wire being a 5v reference, would measuring resistance on the wire be detailed enough to determine if it is damaged?
That would be a good test however this is not a 5V reference wire. It is a signal wire. The issue is not resistance. It’s that it has a voltage on it. Also I did indirectly test resistance on it… when I grounded the signal out it did go to 0V. If the wire had resistance it wouldn’t have gone to 0V.
Would it be possible to de-pin the wire from the connector instead of cutting it by chance?
Matt, you are the BEST. I love you man. Your brilliant deductive approach, humility, sense of humor, and desire to TEACH as you go make you stand way above the crowd. All that and good looks too, lol. "Let's ground out this signal... how is that in any way useful whatever? Uh well, I forgot, NO I remember... " 😂 23:22
Hahaha thanks!! Love you too bro!!
It's a 2017 Chevy. Eric would run down to Wilmer's and get a PCM. You believe PCMs rarely fail, so a junk yard PCM is a reasonable solution for a 2017 Chevy.
I follow SMA also
DIYer here, so don't listen to me too much, but one thing we could have done is to measure resistance, on the connector at the harness side, while unplugged from the PCM, between the signal wire and the rest, right? To check if the signal wire had good isolation from all other wires (obviously it was going to give lower resistance with the 5V reference and the ground of the barometric sensor). But if there was some sort of short circuit with another wire with voltage, it would have appeared as lower resistance I think...
How can there be resistance on the signal wire when the voltage went to zero when I grounded it though?
@@SchrodingersBox No, not when you grounded it. Probably I haven't done a good job explaining myself. What I mean is we could do the same thing that electricians do to the electric installation of a house. They switch off the circuits and check the impedance (resistance in the case of cars) of the line cable with the earth and the neutral with earth. If there is a short circuit or some sort of connection between the cables, instead of infinite or lots of Mohm, you're going to see some KOhms or even ohms. So if you disconnect the connector from the PCM, the resistance between the cables and the barometric signal cable should be close to infinite (with a few exceptions, like the 5V reference for the sensor, etc.). And this checks are done with no voltage applied to anything, we're just checking for some sort of continuity/resistance between cables that should have none, since they should be isolated from each other.
I was screaming bias voltage at my screen the whole time until you showed the control car with a zero volt bias with the connector unplugged (or at least you proved that 0psi does not correspond to 3.3V). I would also check grounds at the PCM as there could technically be a signal ground feeding 3.3V to the computer instead of 0V, but I don't see how that would affect just the baro sensor.
Yes the only choices with connector unplugged would be 0V or 5V depending on the design. Either way 3V is impossible.
@@SchrodingersBox Bias voltage can be any voltage you want (there are videos by Ivan, Paul and Eric O with biases of 2V, 3V and many other voltages on various sensor circuits. It can be done with a voltage divider inside the module), however the impedance associated with this voltage is orders of magnitude higher than what the sensor itself produces, so the sensor should still be capable of pulling this bias down to 0 V or up to 5V.
In your video, you show clear evidence that the PCM is actually supposed to have a 0V bias, rather than 3V, hence the PCM is bad.
Could you check the pin on the PCM for voltage with the connector unplugged?
I did. There was no voltage on it with connector unplugged at PCM. But more importantly we see the voltage drop to zero when wire was cut. This means there was definitely voltage at the pin on the PCM.
You usually can’t look for voltage on the pin when the connector is unplugged because you lose the power feed to the PCM.
@@SchrodingersBox I agree with you: "UNLESS the short was right there inside the PCM connector-- like with some corrosion shorting across the pins. But I assume you looked closely down inside the PCM connectors once you pulled it apart.
Could you have de-pinned the signal wire from the PCM connector instead of cutting it?
Yes I did try that but it wasn’t being very agreeable and I was more concerned about destroying the contact. Much safer and faster to just cut and solder.
Check the resistance to ground on the other vehicle's pcm pin and try that value of resistor for the Malibu
Im not following what that will do exactly- how does that apply for voltage on the wire? I would certainly do that for a suspected high resistance but this is a voltage contamination issue.
I'm confused if voltage went o it would be wire?
Couldn’t you disconnect the pcm connector and do continuity checks with the meter between the yellow wire and all the wires on that particular harness at the pcm? That way you can isolate which wire is shorting together..
Also, what if that voltage is a bias voltage from the pcm used as a diagnostic purpose
No need to we have overwhelming evidence from the ground-out test on every PID that this is not the result of it shorting to a wire externally. It is so much faster to just isolate that signal wire than to check hundreds of pins.
I forgot to ask about the Trans Am
Been looking at the same scanner.
Let me know what you you think about it. How much?
You may have a circuit back feeding into the signal wire
That’s what I was hoping. But at we see this is not possible.
Could the Terrains pcm be close enough to swap for testing to avoid wire cut... then be placed back in terrain without needing some reprogramming...secuirity key etc... Thanks
Yes great idea however Vicki’s car is a V6 and this is a 4 Cylinder.
Thanks so much!
Anytime!
Did you eliminate a bent pin at the ECU connector? Were there any power pins within bent pin range?
How can there a bent pin and be both power and signal return though? Not possible unless each pin is aligned in its slot. Plus all other PCM PIDs were 100% normal and no other codes or issues.
@@SchrodingersBox Thanks. I'll have to look at the video again to see what I missed.... not that I know what happens when you introduce an additional voltage at that point (i.e. at the PCM plug from a bent pin). A series/parallel nightmare. I was thinking perhaps that the normal signal voltage might have been, say, 0.7 volts and, with an additional voltage of 3.3 volts from a foreign source, the signal might have been boosted to 4 volts.
Anyway, as you say, there were no other issues.
The barometric pressure read 15psi you said that's the problem but the scan tool range said 9-16psi is standard ?🤔 I have a top don scanner so I was thinking if the numbers are in that range it good and if it's not it would be red and yall know it's a problem?
It is standard based on barometric pressure. You will never have 15PSI at 6000 feet elevation though. Impossible. It has to be 12.
Am I crazy/wrong? Or could you unplug the connector at the pcm, then check for continuity with a DMM between that baro signal wire and every other wire in that plug ?
Yes I could do that but no need to. So much quicker to just cut the wire and confirm voltage went to zero. There are maybe 200 wires in that PCM- no way I am probing each one lol.
So the dealer would rather pawn it off and not fix problem by replacing pcm? I mean how much a gm pcm cost?
Just looking up.. a refurbished one is only 200 bucks… is the dealer really on some cheap shit?
Did a PCM fix it? Cutting the wire shouldn’t loose voltage if voltage is coming from PCM?? If voltage is lost cutting wire, voltage came from harness? PCM reads the voltage??
You have it backwards. Cutting the wire isolated the signal circuit. If voltage is still there then the voltage source is not from the PCM. But since cutting the wire dropped the voltage, the voltage had to only be from the PCM. There is no other voltage source because it went to zero.
His scope is back probed at the sensor not at the ECM.
Correct!!
It would have been fun to see you crack open the PCM..
Might have been a simple corrosion spot on the board... Maybe next time
I do have a previous where I open the PCM and you can see the damaged transistor.
Choosing to cut it out and jump it as the last step is probably the safest choice you can make. I don't think you touched on bias voltage? If that circuit used bias voltage to verify the integrity of the circuit you would be potentially throwing a PCM at it for nothing! Most people forget that bias voltage isn't constant... it is usually momentarily or when something is unplugged / powered off. Bias voltage is actually how the PCM runs comprehensive monitors to determine if their is a circuit related fault!
There are only two systems used- neither have bias voltage. Either you will have zero V on signal when unplugged or 5V with it unplugged. But in no system for the GM is there 3.3V possible. Either way it’s an internal PCM fault.
@SchrodingersBox bias voltage isn't always in half volt increments. More complicated systems integrate bias voltage on circuits connecting two seperate modules. 19+ ram cummins is a good example of bias voltage that looks like stray voltage. It has bias voltage for both the low and high side drivers that actuate the starter relay. There is no constant ground or power. The PCM supplies the high side and the BCM supplys the low side. If you pull the starter relay out you will get odd readings for bias voltage... but there isn't anything wrong with it. Bias voltage across two modules connected by a starter relay inherintely requires an odd bias voltage because otherwise the starter might sporatically engage when it shouldn't... just an example of bias voltage that might not make sense when you first encounter it...
Correct. I should have said only two systems used on GM of this era specifically. Absolutely some other systems have bias voltage and in fact I have videos showing this on those models.
This model doesn’t have it though.
Why not remove the pin/wire from the connector rather than cut? That would isolate the entire wire and save the repair. 😊
I did try delinking it but was not having success and was more likely to destroy the contact. Cutting was safer. Fixing a wire is easy- solder and heat shrink is a permanent repair.
Often times it’s best to have an extraction tool designed specifically for the connector. Save that, the cut/solder/shrink method is perfect and relatively speedy. Enjoy your content! 🤠🇺🇸
@@thecode3fc I had a recent connector I tried to remove a pin on and I spent WAY too long trying to do it and I'm not sure if the connector is now bad. Where would I find tools to do this? I resorted to a small pick, but it was still too big.
There are depinning kits which basically have really thin tubes that you fit over the pin and it depresses the retention tabs. Kind of like a fuel like disconnect tool. But you have to have exactly the right size or you can damage the pin.
Check the ecm connector for corrosion
That would cause resistance. It won’t produce voltage.
Checking powers and grounds for the ecm would have been 110%.
Dude, it's not "powers and grounds" , it's powers and GROUNDS!
How can there not be power and ground to the PCM? Every single parameter works and the issue is voltage on a signal wire that shows variance. Can’t happen without power and ground on the PCM.
@@SchrodingersBox There are usually multiple power wires and multiple ground wires that feed different parts of the computer. If one power wire has low voltage or bad ground wire strange things can happen inside the computer. Checking those pins easy enough and a best practice kind of thing.
Yes true but we can see clearly this is not a power or ground problem just from the data. It’s not a ground problem because the voltage dropped to zero when I provided external ground- that can’t happen with a good ground. And we know there isn’t a power problem because first, all 5V references were powered and second, there was confirmed 5v ref to this specific circuit. Checking powers and grounds on the PCm would be a waste of time because we know they are good.
That yellow wire can't be unpinned?
I tried but it wasn’t being agreeable. I was more likely to destroy the contact if anything so I decided to not make things worse.
@SchrodingersBox yeah, sometimes they are pretty uncooperative unless you have the exact tool for it.
Possibly de-pin the wire from the pcm connector instead of cutting it? Obviously cutting it is much quicker
Yes many people asked about this. I did try depinning it but I didn’t have the right tool so I was afraid I was more likely to damage the contact. Cutting it was far safer.
@@SchrodingersBox fair play 👍
BIAS voltage?
Lots of people asked that- good though but no. Unplugged you will have only two systems on here- on with no voltage or one with 5V reference that shows up past a resistor. 3.3 is not possible in either.
Hey Matt !!…great diagnosis !!…I too was thinking under the circumstances…CUT THE WIRE !!…LOL !!
C5 Diag
Thanks and wow, I just can’t imagine what I would do without scope man!!!!
Is it not possible that the 3.3v was bias voltage?
Not on a signal wire from a potentiometer. From a Hall effect or inductive maybe, not not a potentiometer. Also we saw there is no voltage present from the same system on the GMC vehicle.
Ok new to the bias stuff. So if I have a car that has voltage on both signal wires with the tps unplugged I have a problem? Thanks for the reply
this was great. i could never do this. now why did the PCM go bad. ha ha
Probably somehow 12V overvoltage to the signal wire. Either the old sensor was broken or an inept technician did something silly with a test light.
VERY good question and absolutely a major concern. As I mentioned many many times, just throwing a PCM in without electrical checks first will likely cause the same issue in the new PCM. Great point, man!!
eric o and royalty do good stuff with no snark or begging
I would watch them then.
I'm at the 39.40 minute mark where you are considering cutting the yellow wire at the PCM. Granted, I'm not a mechanic but an electrician and at this point, I would ohm the yellow wires against all the other wires in the connector because I would assume that none of them should have continuity at all with any of the others. if it does, that would be the wire you would want to chase down to see if it's touching your yellow wire. If it doesn't, I would then turn around and test the pin on the ECU with the key on to see if the voltage is coming from the ECU, if it is, then I would assume it's a bad ECU...There's got to be a better way than cutting the yellow wire, right? Aight, lets see how this ends. *unpause*
There is no way I am ohming 300 wires as opposed to just simply cutting one and confirming the issue and resoldering it. If an electrician is going to literally ohm 300 wires instead of a simple test and permanent repair I would argue I am a way better electrician!!!
Can you de pin the yellow wire?
I tried to but wasn’t able and was afraid I was going to destroy the contact point actually cutting was safer.
@@SchrodingersBox I agree better to cut the wire. whole new can of worms trying to de-pin
ty
Anytime! Thanks for watching.
If cave men could see you now😂
On another level..👍
hahahahaha. well I think that would be funny if a cave man took an Uber up to me and then was only mesmerized after seeing me do this diagnosis hahaha!!!!
@@SchrodingersBox I felt like a cave man watching you :D I'm astoumded everytime I hear you say... I'm not a mechanic hahaha... Im a machine!! 😂😂
Weird how a PCM would go bad, just like that. Maybe a jump-start gone wrong? Would invest in a de-pinning kit though. Or maybe some US-based subscriber can gift you one.
Yeah I have a depinning kit but not of the adapters seemed to fit properly.
@@SchrodingersBox Loose design standards, you gotta hate it. Everyone doing their own thing.
Could you take needle nose pliers and pinch it shut ! ?
Sorry i don’t follow- pinch what?
At least it wasn't the pcv valve
Voltage feeding through a shared ground¿
If it’s feeding through a ground how can it show up on the signal?
Why not open up the ECM, trace that pin into the circuit. Look for any issues, thermal camera. Common faults with that specific ECM
I have previous videos where I show the actual damage to the PCM in cases like this.
My initial guess is corrosion in intermediate connector
what evidence points to that?
@@SchrodingersBox I just started the video, so no evidence just my guess. If green crusties are present, couldnt that introduce voltage from a different wire?
No it would reduce resistance. Not sure I see why guessing without evidence would be in any way fun- seems way more fun to gather the evidence and then formulate a conclusion you know must be correct doesn’t it? Well for me it does. Even if I guess correctly it’s still wrong.
@@SchrodingersBox you’re saying green crusties CANNOT short two wires together? I just like to guess, obviously I test to find out the problem.
After all, using the scientific method - that whole hypothesis part - is your guess? Then you either prove it or disprove it.
Could I pay you to help me troubleshoot ? I have taken data logs and numerous testing watched all your videos multiple times and I just can't figure it out . Thanks
No need to pay. What is the issue and what data do you have. Don’t send me just a data dump- I need relevant data specific to your issue.
@@SchrodingersBox lol I wouldn't dare to with an individual of your expertise . 04 lexus rx330 @ idle LTFT 10% or more increases until I hit around 4000 rpm then they drop to only 4% but constantly dumping fuel never (-)
I have logs with selected PID's being MAF , calc load , rpm , vehicle speed , LTFT , STFT , 02B1S2, 02B2S2 , INJ PW , CYL MIS , TPS , ECT . Recorded during idle , freeway speeds, city speeds .
. I still don’t know what the issue is with the car. Is it a check engine light? Is it running lean? Is it lacking power? I need something to start with here.
@@SchrodingersBox car jerks from 2500 to 4000 rpm then picks up . Had quite a few codes fixed vacuum leaks due to old cracked hoses . Original codes were p0300 and p0430
GM 1.5 turbo. Not exact my know how long life & reliablity...
Yes my understanding is the turbos fail very quickly.
@@SchrodingersBox The Turbo oil lines clog and oil starve/ cook the turbo.
👍
I'm not a mechanic but I play one on UA-cam.
Referring to me?
Get back under the bridge, fam.
So what would a mechanic have done differently than I did? Please explain.
@@SchrodingersBox Was referring to mr. notsohappy. :)
Could’ve just depinned the wire from the computer
Yes many people said that. I did try and wasn’t able to and was more afraid of destroying the contacts. Soldering a wire is easier than replacing the pin if I destroy it.
I wish I could pay for a subscription for the year thanx
I appreciate the feedback. I will consider 1yr subscriptions!!
If you need to clone a used pcm to save some money give me a shout. You could ship them both to me and I can clone it for you.
Oh thank you!! I actually talked them into sending PCM to Flagship One. I have had good luck with them.
32:49... I really liked you grounding your suspect signal and then reading selected pids for change but have an alternate thought. Might you first clear all current error codes and with signal again grounded see if any NEW codes popup. And/or does grounding signal prevent the code of this troubleshooting?
Thanks! I see your thinking but what would happen is I would only get new codes popping up if I changed the PIDs drastically with the ground out of the signal. But I would see the PIDs change so the new codes wouldn’t be relevant anyway. After doing all this the only code was still the P2227 but also a P2229 (I think it was) for a low baro circuit voltage due to grounding it out.
18:18 No Monday morning quarterback here. Personally I would stop now and go directly to the wiring harness, knowing that there is constant voltage. Visual inspection should lead to your problem source, I'd bet.
That's my honest 2 cents. I will watch the rest of the video now to learn what happens.
shoot. that's an odd ball issue. glad I watched to the end.
Yeah we had the same thought but I thoroughly inspected the harness and it was clear the contaminating voltage was definitely from the PCM and not an adjacent wire.
Ummm learn how to follow a test plan, this is a basic 3 wire set up and at most would require 10 minutes of diag. You missed one big step, discount the PCM connector and inspect for moisture intrusion. Wasted 45 minutes of my live watching a chop shop diag !!!!!!
Hahahahahaha well you obviously have no diagnostic skills at all. How would have determined in 10 minutes that this wasn’t a power feed crossover in the harness. I’m waiting for your explanation you idiot.