Nailed it. Been to so many mechanics, had the PCV done, injectors, EVAP, MAF....Paid thousands. Still got the fault code. Had a root round the bay today myself and found and easily found the brake valve hoses were badly cracked!! Just paid $165 bucks for replacement, can't wait to get it in and test it. The cars fuel economy has been terrible for over a year!
Nice review. For those of us who don't do this every day, remembering which way the values are pointing is the first hurdle. Also it's wise to remember whether we are looking at the correction (fuel trim), or raw O2 sensor data. That's mostly a matter of understanding tools, in this case the interface program we are using. Conveniently, when looking at O2 sensor data, higher voltage means rich, and when looking at trim, higher positive numbers mean the system is adding fuel. That similar alignment makes it easier to remember. Of course on the surface it can be confusing since adding fuel is usually a response to a lean condition downstream, which may be completely corrected by the addition of extra fuel. So I see your point, look at trim first because the O2 sensor data may be obscured by correction of injector pulse width. Thanks! Your description of the most common points of failure adds practical guidance to how experienced techs solve problems.
Great video Charles. I remember having a big problem with this on my old 1.8t AWP engine. I replaced the diverter valve because it went bad and when reinstalling the hose on the left side of the diverter valve it was in a slightly different position than it was initially. This caused it to touch what looked to be a metal fuel line behind it. From the heat of the fuel line the rubber hose split open causing a huge leak. I battles this problem for a LONG time and the car always ran in limp mode. Just advice to everyone when working in your car, pay attention to all the details!! Listen to Charles! If i just did a more thorough inspection it would have saved me a lot of time and money. Lesson learned I guess.
Hey HumbleMechanic, I really enjoy this community of channels, I mean You, EricTCG, ScottyK, ChrisFix, and others, this community has really served me well and saved me 1000's of dollars, i'm getting a new clutch atm, paying 1400 for a shop to do it, a HD clutch in my 2002 3.4L V6 Hilux which to me is reasonable, I cannot do that with my tool kit, just before having to surrender my car to the shop, for the first time ever in 5 years it would not start, I have a new battery, it cranked strongly half a dozen times, cranking it for a handful of seconds each time, it did fire up eventually after letting it rest between each attempt and it was rich, tested all the vacuum lines, they were fine, pulled out my MAF sensor, it was dirty, already had the cleaner and turned out that was the problem, MAF was filthy, easy 20 (for the can Co2) fix that, I can only guess what a shop would charge extra. I asked Eric to recommend more Toyota designated Channels and he did name ScottyK, so I would like to ask you the same Q.
Thanks for the kind words to all of us. It really means a lot. This type of thing aint easy, so it's always so warming to hear. I don't really know many Toyota sites. I wish I did LOL, that is like a foreign language to me HAHA
Thank you HumbleMechanic for making this video and your clear explanation. I found my wife's problem through your basic explanation. the last time the Subaru was in the dealership they removed a clamp and never replaced it leaving the air intake the fall off which is what caused the check engine light. I never would have thought to do a visual inspection had I not watched your video. Thank you.
I didn't get that opportunity for visual. I had to feel around the back of the rear most intake hose into the bank 1 throttle body. Rib Rib Gaping hole Rib 😂
"System Lean" means the car is on it's side. Check for overweight driver or passenger, angry mob, earthquake-related fissure, unusual changes in gravity, or acts of god. Not to be confused with "System Rich," which is when you suddenly find yourself driving a Bentley. :D Another great video! Love the visual aid. Who ever thought a giant tube could teach so much?
Such a great video. You explain things so well! I have one of these in the shop right now and I can't wait to get back tomorrow and figure it out.You really make me want to continue my career as a technician.
This video is so perfect. You made me finally understand how all of this works. Great job! My brain always went to vacuum leak in a system lean condition. This gives me much more to think about. Thank you!
Hey Charles, good vid touching a bit on the topic of lean (P0171, P0174) codes focusing on un-metered air and faulty O2's. I Ever give any thought to skewed MAF readings i.e. dirty/ faulty MAF or perhaps issues in the VVT causing lean trouble codes, engine mechanical timing i.e. incorrectly installed timing belt on one cam, sheered key ways etc. or perhaps engine mechanical condition i.e. valve lash etc.? Just curious your thoughts on that and also any thoughts on chasing down lean codes on speed density engines as opposed to MAF engines? Also may keep in mind to that an ignition miss-fire will cause a lean code :) No combustion and all it does is pump air right? HC's can not be read by the O2.
+South Main Auto Repair I have only ran into maybe 2 sys lean caused by mechanical issues. It's sure possible, but not common(in VW land anyway). I agree that there are more issues with system lean. But I think that will be System Lean 202 class. Haha. For the first run of these videos I want to keep it simple to get people mind moving in the right direction. Mostly so thy stop just throwing O2 sensors in.
Wait you mean if I get a lean code I shouldn't just change the AFR's and a fuel pump first ;) Haha Can't wait for Lean Codes 202 :) I have had a few neat case studies on mechanical issues setting lean codes... they can mop the floor with ya if you are not careful! Keep up the good work!
a/b = Q Ideally, Q should have a value 'k', which is a constant for the ideal ratio for your car, but Q represents the real result obtained from conditions a and b. How do you keep Q=k when a and b are changing every few ms? Well if b increases means we divide by a larger number, decreasing our result (Q < k) but we dont want that. We want Q to remain equal to k. In that case, you can increase the value 'a' to compensate the change introduced by increased 'b' On the contrary, if b decreases, we divide by a smaller number, increasing our result (Q > k) For this case, you can decrease the value 'a' to compensate Simple math to understand the fuel/oxygen ratio explanation. Both scenarios have variable values that produce a ratio (Q) which we want to be constant at a value 'k'. In order for the engine to operate at top performance, you have to account for the changing values a and b (fuel and oxygen) at every detonation, on every cylinder.
You aren't going to have a vacuum leak before the throttle plate. You will however have an air metering error comparing the intake mass air vs O2 reading. The idle air control valve could cause this issue as well being it's a controlled vacuum leak.
I have a Chevy Silverado with 4.3 liter engine started missing one night check engine lite came on system lean bank 1 short term 55 long term 25 no vacuum leaks. Suspect a bad 02 sensor before cat and looks like that's what your saying in video. Thanks for showing
Getting a P12A2 at the same time. Cold start misfires first (most likely carbon), warm engine, clear codes then get P0171 and sometimes P12A2. Fuel filter has not been changed for a while
I just had this happen on a car I bought, turns out the previous owner must have had an intake kit on the car and then shoved the old standard intake on before I got it and forgot to mention he had somehow sliced a big gash in the underside of the intake pipe causing a massive vacuum leak that I couldn’t see until I removed it.
I have been dealing with this code for about a month now on my 99 yukon. I have checked and cleaned everything i could. Just found the problem yesterday and it was that the exhaust flange gasket deteriorated away and it is located right before the o2 sensor.
So on an MK4 (2001) Jetta (1.8T AWW), how many drive cycles will it take the CEL to reset on its own (After a fix)? I did the stupid thing when I first bought this car (because I wasn't sure I was going to keep the car...) - I bought a $19.00 MAF from ebay. It only lasted 8 months, and then began (even after cleaning) under-reporting airflow, causing an intermittent P0171 code every time the LTFT hit 20% (Under ALL engine loads). Today, I installed a Bosch MAF, and cracked a smile when it entered closed loop, and STFT immediately pegged at -20% while the +20% LTFT began dropping. 3 drive cycles later, I have less than 8% LTFT and still have some negative STFT, which is still working on bringing that LT number down. I'm confident the problem is fixed, but wondered how long it will take the ECU to figure out that the problem is fixed and clear the CEL. Figured I'd ask a VW man :-)
Great video, I have the P0171 code on my 97 Oldsmobile and on top of that the car doesn't start half the time. I changed the fuel filter like 10k miles ago and the car has 120k miles. I'm thinking since the car doesn't start half the time it might be the Fuel pump. Any Idea if it can be something else. Thanks
What would be the cause of a lean condition from using E85 in a non flex fuel vehicle. From what I've gathered for my vehicle, is that it's burning more efficiently or cleaner, or faster. Could it be that my vehicle is not pumping enough of the E85 to be efficient?
Hey Charls.. keep up the good work. i watch your videos probably 3-4 times to make sure i get everything you say. because there are so much information to absorb as a student mechanic. thanks for all the information (Y) good luck
I have 1500cc petrol engine in toyota ...... I tried two maf sensor one giving 1.3 g/s at 650 rpm.... Another giving 1.7 g/s at 650 rpm.... Which one should i use for better fuel economy.....plz reply
Can an OBDII diagnostic alone can determine the exact cause of 'system lean' error code? Also, if the fault is with the oxygen sensor, is it best to replace both (I know there are 4 in a normal car) one before the catalytic sensor and one after? even if the second one is not faulty? Thank you for the great informative videos. Subscribed!
Hey, I have a old peugeot 106, And my car will idle rough when sat in traffic, I've put a new icv valve and oxygen sensor on cleaned the carburetor with no luck, i have noticed after changing the spark plugs noticed they are coated white. Does this mean it's lean on fuel? It drives fine other than this fault
Engine runs lean after replacing the oxygen sensor. In the first 15 to 20minutes vehicle accelerates fine but after heated up it hesitates and vehicle doesn't rev up. The sensor is genuine and bought from the agent. What may cause this problem?
Smart guy. Great details. And if I was a mechanic or Am aspiring one, I Might have understood a tiny bit of that. Nope. I watched to see of I could learn how serious this is in the short term....onto the next search result.
i replaced my o2 sensor problem i put in crocked because some striped the treads my screen on the 02 sensor screen on the end got crushed and it spines could that cause o2 sensor to fail
Would old gas cause this condition? I found my pcv tube that went into the cold air intake loose and barely in creating a vacuum leak. When this happened my idle was rough and stabilitrak light came on. I didnt think I would make it home. My spark plugs were fouled. I cleaned them all and fixed the pcv tube leak with zip ties. I drove the vehicle several days later and it idled fine but my check engine light is now on and it gave me codes p2096 and p2098 lean fuel trims bank 1 and 2. With these codes set is that from the previous issue (vacuum leak) or is this now another issue (possible bad gas)?
2 cylinders read bad st autozone.. Changed out coils... All coils going out over time.. 2001 f250. Changed last ones almost, after changed, went to autozone, had system lean and both cylinder reads.. Was not 250 miled yet to reset. Was reading from O2 sensor.. Will a coil issue cause a system lean reading from the 02? My heat is also jacked up.. Am wondering if low coolant levels could cause that. After coils failed, would see smoke coming out of engine.. Looked like a leak somewhete possible but dont know
Mr. Humble Mechanic, I need help. I have a 2010 Volkswagen CC sport with the 2.0 TSI engine. I have a check engine light on and also the EPC light is on. I had my car scanned at the auto store. It has a P0302 and a P2187 codes showing. Any ideas?
I have questions so I have a Toyota 4 runner and I got a crack in the radiator housing holes so it broke off where you connect the hose up to the radiator so I have to get a hold of the radiator. But could that be a problem as well is P0171 code popped up? I had checked all the holes and I noticed the the crack was at
P0171 code, my car when it's cold will start right away but if I let it cold for 15 min wont start or will have a very hard time to start. I had spark plugs oil on them, I change the spark plugs and valve cover gasket, fuel filter, the mass air sensor.
Great video. I'm afraid I fall into the diy camp of changing a long list of parts on my 2008 Audi a4 2.0t fsi, and not fixing the problem. I also had it at a local shop that said they did a fuel pressure test and a smoke test, and couldn't find the problem. Not an Audi specialist. Wonder if I need to give up and pay the dealer the 169.00 to diagnose the problem. I changed the MAF, purge valve, checked the hpfp and changed the cam follower even though the one in there looked fine. Changed plugs, Mercedes fuel system cleaner, fuel filter, pcv crack case thing, pcv hoses. After changing the pcv hoses it got better, but still comes back after a long drive (over an hour) and only shows at idle. Lumpy, almost dies but doesn't. Otherwise runs great off idle. I am stumped. Only throws P0171, no other code.
Hi David i done the same as you 2007 Audi A3 1.8T , my engine runs fine , then one day i notice a check engine light , hooked up the scan tool and it was a P0171 , first thing i changed was PVC valve , MAF sensor , air filter , fuel filter , i cleared the code every single time but comes back , buy this time im getting confused , take it to garage they hook up smoke machine they said it was your rear main seal and showed me where the smoke was coming out , so i thought i would try some Rislone rear main seal repair oil and it has stop the slow oil leak i had but the engine light still comes on??? ,
@@karlhendricks8864 Thanks for the comment Karl. It's been fixed for several years now thankfully. The problem was what I will call a breather/vent hose that I believe goes between the crankcase and manifold. On the 2008 2.0, it is a silver metal formed hose toward the front passenger side on the engine. A German mechanic told my mechanic to take it off and blow through it from both ends. Apparently there is a valve in the middle of the hose you can't see that should stop air flowing in one direction. Since the mechanic could blow in both directions it acted like a vacuum leak which usually is far worse at idle since there is little fuel being demanded. A new hose fixed it. Not sure if that crank case vent hose is on the 1.8 or not.
Hey man, I recently purchased a 2015 Infiniti Qx50 3.7L V6, i got a MAF and Lean sys error. Took it back to the dealer and they mentioned they changed the Air filter was really dirty and etc. so they changed that. The code came back and this time they told me i have to change my spark plugs, i did that today since they were almost at the end of their life cycle being use for almost 100k miles. I have not had any codes so far but what i wanted to ask is whether a faulty spark plug could possibly cause this code?
Hello. I have a problem with sucking in fake air. it shows a value of +20-25%. the probes are new. code p4091 p0492 p0171 p0174. can code p40.. be related to it? golf mk5 r32
I recently replaced my 02s. Forgot to disconnect the ground from my battery caused a short. Obviously... my Taurus blew the fuse under the hood. Number 28. Made the rookie mistake of climbing over the engine and working the intake loose. Long story short check your. vacs your codes and double check your own work.
What the hell? Why would you disconnect the battery to disconnect a o2 sensor? Just keep your car key in your pocket thats more than enough to disconnect the o2 sensor without going anything wrong
I have a 2011 Audi A5 Quattro 2.0T It’s running too lean only in cold weather the ltft 40% ,, when I hit the gas it goes down to 10 ,12when the car gets worm it’s back to 13 % Is it possible to have a vacuum leak or where should I look thank you - parts have been changed 1.pcv valve oem
I just changed a coil and all sparkplugs after a misfire issue, it was running good for a few days and now, now I have a system lean code coming up and I’m losing lots of power. Any thoughts?
I have 08 Passat 2.0T 122k miles. CEL is on. P0302 P0171. CEL is on. I changed all sparks/coil. And now the CEL is still on for P0171 system 1 too lean bank 1. But after changing spark/coil. I get a random misfire with the random shaking sound from exhaust then white smoke coming out. Can it be the 02 sensor (downstream) that’s causing my misfire and system to lean?
I have a 2010 cc 2.0t, on new and old maf sensor the same p0101 on idle short trim 25% longtrim 0 for about 2min to 5 min until warms up, then short gets to 4-8 and long 40 - 49 on idle for 3min and on idle stabilized to short trim 0 - 48 long trim. It could be the wires? Intake No leaks the turbo whistle when driving and missfires p0300 to 0304 and the p0101 codes don't think is the cat plugged but Not sure. Thank you in advance.
Great name btw!! Quick question kind sir. If i'm planning on replacing my oem header and oem catback exhaust, would that affect how my car will run, lean or rich? without it being (tuned)
I have toyota solara 2004 v6 egine. There are are two faulty oxygen sensors . Do these faulty sensors cause a system lean? Or can it be something else as well? It seems that its takes a while for my car to pick up speed. Any suggestions.
Oh last thing,last year my turbo blow and dumped loads and loads of oil in the exhaust.....when I pulled the down pipe off to change the turbo I notice the whole of the turbine and shaft had gone never to be seen again could this be blocking the exhaust or could the oil of mucked it up to?Cheers mate
About a year ago I had some 02 codes on my v6. Ended up replacing all 4 o2 sensors. 6 coils. 1 cat converter and inlet manifold gasket. All good for 6 months now I'm getting bank 1 and 2 lean at idle codes..... All the long and short trim figures look good. What could it be ?????
Hi Humble, my 2006 Jettta 2.5 has the tendacy to reve up when stopped or idle, the RPM would rise without my pressing gas. My engine light is on, but still drives. Also my fuel gauge shows empty yet i have gas, drives and fuel light is not on. Please help. I love this car, so i am gonna invest.
Where can you go to view your vehicle's numeric values if you look at it from a Snap-On tablet or the computer things that show all the stuff like at 2:55?
my long term fuel trim whas 12 % the car had no fault codes, but the performance of the engine really sucked! After checking for false air and replacing all filters still the same. So at the end i replaced the front o2 sensor with a new oem one. And now the car feels like a whole new car a lott lots of power and the long term stays at 0,5 %. Never trust these lying sensors !
this is probably what wrong with my car. it wont even rev past 2000 rpms it drives fine just cut off if u dont let it warm up. im gonna change the 02 first while also checking for leaks. its an 05 ls lincoln i bet this does the trick
friend just had the issue turns out Brake booster was rusted and allowing air in, Pinching the vacuum line to the booster proved the issue at the booster was the cause
P0171 I would like to add something to this that i just experienced. I have the n249 delete sia delet etc. And this code gave me the run around for weeks. Smoke test leak test everything. Well because of those deletes i have bypassed my diverter vacuum line to the throttle body next to bank 1. Well the vacuum side of the diverter when out and was allowing boost pressure to enter after the trottle body right into bank 1. Long story short. New diverter valve fixed it. Sad part about this is a smoke test wont show it
My A/F ratio is showing 18-20 Air fuel ratio. Its a single turbo fresh build Infiniti G35. You think I can just bring it for tuner to adjust it? Fresh built engine.
What about a system lean during a specific condition? Like at idle? Would that be considered a vacuum leak/excessive air, or would we go more into fuel delivery? Or O2 sensor?
I had 2 codes on my Audi A4 Sedan B8 1.8TSI p2293 and p0243 I did change the high pressure feul pump and turbo Solenoid all codes gone but now having new code P0171 any advice the car drive but not 100% full power any advice please
When you said that O2 sensor TYPICALLY but not ALWAYS peg out at max LEAN signal, I'm fairly certain it's based on your own personal experiences exclusively, and not influenced by what you have heard from others... My question is, how much of that supporting experience comes from ONLY V.W. / Audi ??? My gut tells me better than 75% stems solely from VW. Only reason I even bring this up at all is because based on my experience at independent shops where I have worked on just about ANY make and model of car in existence, it's a fairly even 50/50 split for O2 sensors to peg out either lean or rich when it kicks the bucket. I have yet to really find any rhyme or reason as to the causes of either death result... I feel a SLIGHT bias of Rich codes in American vehicle like Ford and GM. It may not even be real and if it is real, it's very very slight...
Hey, I have a question. Is it possible that Longtube headers and no catalytics on my 1999 Mustang GT are causing a lean condition? Ive changed alot to stock as i bought it modded. Only thing aftermarket is those headers. Also I will have the PCM Reflashed at ford to the stock flash in case the tuner I used didnt do the job right, just to start with a clean slate. Revving the engine repeatedly makes the fuel trims go down from 25% to 10-17% idling until I leave it idle too long then they rise again.
Hey Charles, great video by the way. Broda i have a misfire that starts when the engine is at working temp. After i downshift at aceleration. Mostly at 2nd and 3rd gear. Spark plugs are new, cables as well. ( its a Seat leon 1.4 16v axp engine 2002). The fuel pump resistance gives me 3.5 ohms. According to the info i have seen that it should not be over 3 ohms. So im starting to think that is the fuel pump that when it gets hot dosent reach the minimun pressure. And the mixture gets lean. What do you think or what would you do for this case. Thanks a lot, and sorry to disturb. God bless you.
Man so much good information, great video. Quick question, they did a fuel decarbonation and fuel duct cleaning and my car is back firing at idle and acceleration, is that normal for the first few days?
I have saturn ion i put a short ram intake in but there is a secondary air injection hose out and i get a check egine light idk to replace it back to stock or try n remove the hose
I replaced the O2 sensor because a mechanic told me to replace it. Did not fix the problem. Is replacing the 02 sensor first the best choice. The scanner said running lean Bank 1.
![Engine Fault Code P0171 - System Too Lean Bank 1! [Symptoms, Causes, and Fixes]](/img/n.gif)
Nailed it. Been to so many mechanics, had the PCV done, injectors, EVAP, MAF....Paid thousands. Still got the fault code. Had a root round the bay today myself and found and easily found the brake valve hoses were badly cracked!! Just paid $165 bucks for replacement, can't wait to get it in and test it. The cars fuel economy has been terrible for over a year!
please let us know if it worked!
Nice review. For those of us who don't do this every day, remembering which way the values are pointing is the first hurdle. Also it's wise to remember whether we are looking at the correction (fuel trim), or raw O2 sensor data. That's mostly a matter of understanding tools, in this case the interface program we are using. Conveniently, when looking at O2 sensor data, higher voltage means rich, and when looking at trim, higher positive numbers mean the system is adding fuel. That similar alignment makes it easier to remember. Of course on the surface it can be confusing since adding fuel is usually a response to a lean condition downstream, which may be completely corrected by the addition of extra fuel. So I see your point, look at trim first because the O2 sensor data may be obscured by correction of injector pulse width. Thanks! Your description of the most common points of failure adds practical guidance to how experienced techs solve problems.
Great video Charles. I remember having a big problem with this on my old 1.8t AWP engine. I replaced the diverter valve because it went bad and when reinstalling the hose on the left side of the diverter valve it was in a slightly different position than it was initially. This caused it to touch what looked to be a metal fuel line behind it. From the heat of the fuel line the rubber hose split open causing a huge leak. I battles this problem for a LONG time and the car always ran in limp mode. Just advice to everyone when working in your car, pay attention to all the details!! Listen to Charles! If i just did a more thorough inspection it would have saved me a lot of time and money. Lesson learned I guess.
Hey HumbleMechanic, I really enjoy this community of channels, I mean You, EricTCG, ScottyK, ChrisFix, and others, this community has really served me well and saved me 1000's of dollars, i'm getting a new clutch atm, paying 1400 for a shop to do it, a HD clutch in my 2002 3.4L V6 Hilux which to me is reasonable, I cannot do that with my tool kit, just before having to surrender my car to the shop, for the first time ever in 5 years it would not start, I have a new battery, it cranked strongly half a dozen times, cranking it for a handful of seconds each time, it did fire up eventually after letting it rest between each attempt and it was rich, tested all the vacuum lines, they were fine, pulled out my MAF sensor, it was dirty, already had the cleaner and turned out that was the problem, MAF was filthy, easy 20 (for the can Co2) fix that, I can only guess what a shop would charge extra. I asked Eric to recommend more Toyota designated Channels and he did name ScottyK, so I would like to ask you the same Q.
Thanks for the kind words to all of us. It really means a lot. This type of thing aint easy, so it's always so warming to hear. I don't really know many Toyota sites. I wish I did LOL, that is like a foreign language to me HAHA
just had this issue, my PCV system had big cracks and vacuum leaks. don't forget to look there also!
Thank you HumbleMechanic for making this video and your clear explanation. I found my wife's problem through your basic explanation. the last time the Subaru was in the dealership they removed a clamp and never replaced it leaving the air intake the fall off which is what caused the check engine light. I never would have thought to do a visual inspection had I not watched your video. Thank you.
Visual inspection… yep, I found the problem and fixed it! Thanks very much Charles for another super-informative video. Keep ‘em coming!
I didn't get that opportunity for visual. I had to feel around the back of the rear most intake hose into the bank 1 throttle body.
Rib
Rib
Gaping hole
Rib
😂
I don’t know much about cars but this video has helped me tremendously in understanding what’s wrong with my car. Thank you
This is an awesome video Charles. I don't know how many times I've seen people throw o2 sensors at a vehicle with P0171 and 174 without any diag.
"System Lean" means the car is on it's side. Check for overweight driver or passenger, angry mob, earthquake-related fissure, unusual changes in gravity, or acts of god. Not to be confused with "System Rich," which is when you suddenly find yourself driving a Bentley. :D
Another great video! Love the visual aid. Who ever thought a giant tube could teach so much?
Such a great video. You explain things so well! I have one of these in the shop right now and I can't wait to get back tomorrow and figure it out.You really make me want to continue my career as a technician.
This video is so perfect. You made me finally understand how all of this works. Great job! My brain always went to vacuum leak in a system lean condition. This gives me much more to think about. Thank you!
Hey Charles, good vid touching a bit on the topic of lean (P0171, P0174) codes focusing on un-metered air and faulty O2's. I Ever give any thought to skewed MAF readings i.e. dirty/ faulty MAF or perhaps issues in the VVT causing lean trouble codes, engine mechanical timing i.e. incorrectly installed timing belt on one cam, sheered key ways etc. or perhaps engine mechanical condition i.e. valve lash etc.? Just curious your thoughts on that and also any thoughts on chasing down lean codes on speed density engines as opposed to MAF engines? Also may keep in mind to that an ignition miss-fire will cause a lean code :) No combustion and all it does is pump air right? HC's can not be read by the O2.
+South Main Auto Repair I have only ran into maybe 2 sys lean caused by mechanical issues. It's sure possible, but not common(in VW land anyway).
I agree that there are more issues with system lean. But I think that will be System Lean 202 class. Haha.
For the first run of these videos I want to keep it simple to get people mind moving in the right direction. Mostly so thy stop just throwing O2 sensors in.
Wait you mean if I get a lean code I shouldn't just change the AFR's and a fuel pump first ;) Haha Can't wait for Lean Codes 202 :) I have had a few neat case studies on mechanical issues setting lean codes... they can mop the floor with ya if you are not careful! Keep up the good work!
+South Main Auto Repair ERIK O FOR PREZZ LOL
South Main Auto Repair Saturno Outlook
Saturno Outlook 2008
a/b = Q
Ideally, Q should have a value 'k', which is a constant for the ideal ratio for your car, but Q represents the real result obtained from conditions a and b.
How do you keep Q=k when a and b are changing every few ms?
Well if b increases means we divide by a larger number, decreasing our result (Q < k) but we dont want that. We want Q to remain equal to k.
In that case, you can increase the value 'a' to compensate the change introduced by increased 'b'
On the contrary, if b decreases, we divide by a smaller number, increasing our result (Q > k)
For this case, you can decrease the value 'a' to compensate
Simple math to understand the fuel/oxygen ratio explanation.
Both scenarios have variable values that produce a ratio (Q) which we want to be constant at a value 'k'. In order for the engine to operate at top performance, you have to account for the changing values a and b (fuel and oxygen) at every detonation, on every cylinder.
Really feel like I can be a mechanic after watching this 😶😳🥰
no you can't.... what you 'feel' is imagination and very different from actually doing work with tools correctly.
Doug H. in VA shut up Doug 🙄
Doug H. in VA yeah, shut up Doug. 😂
@@DougHinVA no 8
You belong in the kitchen!
That Integrated Engineering intake looks awesome!!
You aren't going to have a vacuum leak before the throttle plate. You will however have an air metering error comparing the intake mass air vs O2 reading. The idle air control valve could cause this issue as well being it's a controlled vacuum leak.
I had this on my Toyota 3.4L V6, it was the Mass Air Flow Sensor, cleaning helped, replacing fixed it.
NCIE
How long after you cleaned it did you just decide to replace it ?
I have a Chevy Silverado with 4.3 liter engine started missing one night check engine lite came on system lean bank 1 short term 55 long term 25 no vacuum leaks. Suspect a bad 02 sensor before cat and looks like that's what your saying in video. Thanks for showing
Easy to understand that is a gas guzzler nightmare! Great video 👍
Getting a P12A2 at the same time. Cold start misfires first (most likely carbon), warm engine, clear codes then get P0171 and sometimes P12A2. Fuel filter has not been changed for a while
You're a great educator my friend
Clear and concise
Thank you
I just had this happen on a car I bought, turns out the previous owner must have had an intake kit on the car and then shoved the old standard intake on before I got it and forgot to mention he had somehow sliced a big gash in the underside of the intake pipe causing a massive vacuum leak that I couldn’t see until I removed it.
I have been dealing with this code for about a month now on my 99 yukon. I have checked and cleaned everything i could. Just found the problem yesterday and it was that the exhaust flange gasket deteriorated away and it is located right before the o2 sensor.
So on an MK4 (2001) Jetta (1.8T AWW), how many drive cycles will it take the CEL to reset on its own (After a fix)? I did the stupid thing when I first bought this car (because I wasn't sure I was going to keep the car...) - I bought a $19.00 MAF from ebay. It only lasted 8 months, and then began (even after cleaning) under-reporting airflow, causing an intermittent P0171 code every time the LTFT hit 20% (Under ALL engine loads). Today, I installed a Bosch MAF, and cracked a smile when it entered closed loop, and STFT immediately pegged at -20% while the +20% LTFT began dropping. 3 drive cycles later, I have less than 8% LTFT and still have some negative STFT, which is still working on bringing that LT number down. I'm confident the problem is fixed, but wondered how long it will take the ECU to figure out that the problem is fixed and clear the CEL. Figured I'd ask a VW man :-)
Is it true that TFSI engine runs lean at idle? So with 1.25 reading instead of stoichiometric 1.0 ?
i like this guy, he’s very detailed and knowing what he is saying.
Thank you
bro please answer some of these questions they pertain to others as well
I answered that question on O2 sensors in a reply to the person that asked.
Great video, I have the P0171 code on my 97 Oldsmobile and on top of that the car doesn't start half the time. I changed the fuel filter like 10k miles ago and the car has 120k miles. I'm thinking since the car doesn't start half the time it might be the Fuel pump. Any Idea if it can be something else. Thanks
My son has an aftermarket exhaust with no catalytic converter and he is getting the po171 code. Could removing the cat cause that code ?
What would be the cause of a lean condition from using E85 in a non flex fuel vehicle. From what I've gathered for my vehicle, is that it's burning more efficiently or cleaner, or faster. Could it be that my vehicle is not pumping enough of the E85 to be efficient?
Will a fuel pump not being tight for a 2005 highlander give code P0171? I replaced fuel pump and not sure if that's what it is..
Hey Charls.. keep up the good work. i watch your videos probably 3-4 times to make sure i get everything you say. because there are so much information to absorb as a student mechanic. thanks for all the information (Y) good luck
Thanks so much for the kind words. Glad to be able to help.
4:25 then why are there many videos showing a P2096 fixed after properly clipping a loose air box? Very confused. Please help.
I have a kia fote ex 2012 with P 2191 code what should I check
does weak fuel pump can make the engine issue to be a high gas consumption??
I have 1500cc petrol engine in toyota ......
I tried two maf sensor one giving 1.3 g/s at 650 rpm....
Another giving 1.7 g/s at 650 rpm....
Which one should i use for better fuel economy.....plz reply
Can an OBDII diagnostic alone can determine the exact cause of 'system lean' error code?
Also, if the fault is with the oxygen sensor, is it best to replace both (I know there are 4 in a normal car) one before the catalytic sensor and one after? even if the second one is not faulty?
Thank you for the great informative videos. Subscribed!
Hey, I have a old peugeot 106, And my car will idle rough when sat in traffic, I've put a new icv valve and oxygen sensor on cleaned the carburetor with no luck, i have noticed after changing the spark plugs noticed they are coated white. Does this mean it's lean on fuel? It drives fine other than this fault
Engine runs lean after replacing the oxygen sensor. In the first 15 to 20minutes vehicle accelerates fine but after heated up it hesitates and vehicle doesn't rev up. The sensor is genuine and bought from the agent. What may cause this problem?
So what are the costs differences to get this fixed? I'm hearing anywhere from about $50-$100 up to $1000.
Yes. It depends on the issue. There are tons of things that can cause a system lean
Can a missing gas cap cause it as well ?? Reason why is because lost my gas cap then that code came up
Smart guy. Great details. And if I was a mechanic or Am aspiring one, I Might have understood a tiny bit of that. Nope. I watched to see of I could learn how serious this is in the short term....onto the next search result.
It can be minor or major. Totally depends
i replaced my o2 sensor problem i put in crocked because some striped the treads my screen on the 02 sensor screen on the end got crushed and it spines could that cause o2 sensor to fail
Seems like my 2006 silverado is running lean but I have no codes. Can it be the catalytic converter? My rpms are low. Transmission is fine.
This man is so intelligent
Would old gas cause this condition? I found my pcv tube that went into the cold air intake loose and barely in creating a vacuum leak. When this happened my idle was rough and stabilitrak light came on. I didnt think I would make it home. My spark plugs were fouled. I cleaned them all and fixed the pcv tube leak with zip ties. I drove the vehicle several days later and it idled fine but my check engine light is now on and it gave me codes p2096 and p2098 lean fuel trims bank 1 and 2. With these codes set is that from the previous issue (vacuum leak) or is this now another issue (possible bad gas)?
2 cylinders read bad st autozone.. Changed out coils... All coils going out over time.. 2001 f250. Changed last ones almost, after changed, went to autozone, had system lean and both cylinder reads.. Was not 250 miled yet to reset. Was reading from O2 sensor.. Will a coil issue cause a system lean reading from the 02? My heat is also jacked up.. Am wondering if low coolant levels could cause that. After coils failed, would see smoke coming out of engine.. Looked like a leak somewhete possible but dont know
Mr. Humble Mechanic, I need help. I have a 2010 Volkswagen CC sport with the 2.0 TSI engine. I have a check engine light on and also the EPC light is on. I had my car scanned at the auto store. It has a P0302 and a P2187 codes showing. Any ideas?
I have questions so I have a Toyota 4 runner and I got a crack in the radiator housing holes so it broke off where you connect the hose up to the radiator so I have to get a hold of the radiator. But could that be a problem as well is P0171 code popped up? I had checked all the holes and I noticed the the crack was at
P0171 code, my car when it's cold will start right away but if I let it cold for 15 min wont start or will have a very hard time to start. I had spark plugs oil on them, I change the spark plugs and valve cover gasket, fuel filter, the mass air sensor.
What does code P2191 System too lean at higher load bank 1 need to be fixed?
And is it safe to drive long distance with a yellow engine light on?
My Beetle shakes at 60mph. Just got new tires, alignment, and a tune up. Any suggestions why its shaking bad?
Great video. I'm afraid I fall into the diy camp of changing a long list of parts on my 2008 Audi a4 2.0t fsi, and not fixing the problem. I also had it at a local shop that said they did a fuel pressure test and a smoke test, and couldn't find the problem. Not an Audi specialist. Wonder if I need to give up and pay the dealer the 169.00 to diagnose the problem. I changed the MAF, purge valve, checked the hpfp and changed the cam follower even though the one in there looked fine. Changed plugs, Mercedes fuel system cleaner, fuel filter, pcv crack case thing, pcv hoses. After changing the pcv hoses it got better, but still comes back after a long drive (over an hour) and only shows at idle. Lumpy, almost dies but doesn't. Otherwise runs great off idle. I am stumped. Only throws P0171, no other code.
Hi David i done the same as you 2007 Audi A3 1.8T , my engine runs fine , then one day i notice a check engine light , hooked up the scan tool and it was a P0171 , first thing i changed was PVC valve , MAF sensor , air filter , fuel filter , i cleared the code every single time but comes back , buy this time im getting confused , take it to garage they hook up smoke machine they said it was your rear main seal and showed me where the smoke was coming out , so i thought i would try some Rislone rear main seal repair oil and it has stop the slow oil leak i had but the engine light still comes on??? ,
@@karlhendricks8864 Thanks for the comment Karl. It's been fixed for several years now thankfully. The problem was what I will call a breather/vent hose that I believe goes between the crankcase and manifold. On the 2008 2.0, it is a silver metal formed hose toward the front passenger side on the engine. A German mechanic told my mechanic to take it off and blow through it from both ends. Apparently there is a valve in the middle of the hose you can't see that should stop air flowing in one direction. Since the mechanic could blow in both directions it acted like a vacuum leak which usually is far worse at idle since there is little fuel being demanded. A new hose fixed it. Not sure if that crank case vent hose is on the 1.8 or not.
Wow that's good you have it sorted out , and it was just one breather hose ! Maybe I will check mine
Hey man, I recently purchased a 2015 Infiniti Qx50 3.7L V6, i got a MAF and Lean sys error. Took it back to the dealer and they mentioned they changed the Air filter was really dirty and etc. so they changed that. The code came back and this time they told me i have to change my spark plugs, i did that today since they were almost at the end of their life cycle being use for almost 100k miles. I have not had any codes so far but what i wanted to ask is whether a faulty spark plug could possibly cause this code?
Hello. I have a problem with sucking in fake air. it shows a value of +20-25%. the probes are new. code p4091 p0492
p0171 p0174. can code p40.. be related to it?
golf mk5 r32
I have a 99 Toyota Corolla ce and Im getting that same code P0171 what should be the first thing to check
Vacuum leaks look for loose and add tape to the male end or cut off the end of the vacuum line that has stretched or replacing the vacuum line.
I recently replaced my 02s. Forgot to disconnect the ground from my battery caused a short. Obviously... my Taurus blew the fuse under the hood. Number 28. Made the rookie mistake of climbing over the engine and working the intake loose. Long story short check your. vacs your codes and double check your own work.
What the hell? Why would you disconnect the battery to disconnect a o2 sensor? Just keep your car key in your pocket thats more than enough to disconnect the o2 sensor without going anything wrong
I have a 2011 Audi A5 Quattro 2.0T
It’s running too lean only in cold weather the ltft 40% ,, when I hit the gas it goes down to 10 ,12when the car gets worm it’s back to 13 %
Is it possible to have a vacuum leak or where should I look thank you
- parts have been changed
1.pcv valve oem
I just changed a coil and all sparkplugs after a misfire issue, it was running good for a few days and now, now I have a system lean code coming up and I’m losing lots of power. Any thoughts?
I have 08 Passat 2.0T 122k miles. CEL is on. P0302 P0171. CEL is on. I changed all sparks/coil. And now the CEL is still on for P0171 system 1 too lean bank 1. But after changing spark/coil. I get a random misfire with the random shaking sound from exhaust then white smoke coming out. Can it be the 02 sensor (downstream) that’s causing my misfire and system to lean?
I have a 2010 cc 2.0t, on new and old maf sensor the same p0101 on idle short trim 25% longtrim 0 for about 2min to 5 min until warms up, then short gets to 4-8 and long 40 - 49 on idle for 3min and on idle stabilized to short trim 0 - 48 long trim. It could be the wires?
Intake No leaks the turbo whistle when driving and missfires p0300 to 0304 and the p0101 codes don't think is the cat plugged but Not sure.
Thank you in advance.
Great name btw!!
Quick question kind sir.
If i'm planning on replacing my oem header and oem catback exhaust, would that affect how my car will run, lean or rich?
without it being (tuned)
So i had a p0089 code yesterday and later followed by a p0171 could this be something like a fuel filter/fuel pressure regulator issue causing this?
I have toyota solara 2004 v6 egine. There are are two faulty oxygen sensors . Do these faulty sensors cause a system lean? Or can it be something else as well? It seems that its takes a while for my car to pick up speed. Any suggestions.
How bout a short in a sensor wire. Could it cause problems with other sensors in the same part of the system?
Oh last thing,last year my turbo blow and dumped loads and loads of oil in the exhaust.....when I pulled the down pipe off to change the turbo I notice the whole of the turbine and shaft had gone never to be seen again could this be blocking the exhaust or could the oil of mucked it up to?Cheers mate
How bad is it to keep driving my 05 chevy cobalt for now until i have someone look at it
Hey Charles any chance of a video on system rich
Hi charol I own a 2010 Tiguan I put tow set of brand new spark plug turn black sooded on the tip top of spark plug and misfires help me please
well said explanation on fuel trim percentages
So my A3 has a BGU engine, no MAF sensor, and a lean condition, fuel issue?
what if your running lean with out being on Wide open throttle? also having lean issues after rev down ..so rev it as it goes down ..runs lean
So with lets say + 25 lean code if 02 was bad would ECM send 02 code also with lean code?
About a year ago I had some 02 codes on my v6. Ended up replacing all 4 o2 sensors. 6 coils. 1 cat converter and inlet manifold gasket. All good for 6 months now I'm getting bank 1 and 2 lean at idle codes.....
All the long and short trim figures look good.
What could it be ?????
Hi Humble, my 2006 Jettta 2.5 has the tendacy to reve up when stopped or idle, the RPM would rise without my pressing gas. My engine light is on, but still drives. Also my fuel gauge shows empty yet i have gas, drives and fuel light is not on. Please help. I love this car, so i am gonna invest.
Would a bad upstream air fuel meter that correcting at 35% drop the correction to almost normal at WOT?
Where can you go to view your vehicle's numeric values if you look at it from a Snap-On tablet or the computer things that show all the stuff like at 2:55?
Hi I replaced my turbocharged, and got p0171 and p0101. And cannot build boost. Waste gate is opening to soon
my long term fuel trim whas 12 % the car had no fault codes, but the performance of the engine really sucked! After checking for false air and replacing all filters still the same. So at the end i replaced the front o2 sensor with a new oem one. And now the car feels like a whole new car a lott lots of power and the long term stays at 0,5 %. Never trust these lying sensors !
this is probably what wrong with my car. it wont even rev past 2000 rpms it drives fine just cut off if u dont let it warm up. im gonna change the 02 first while also checking for leaks. its an 05 ls lincoln i bet this does the trick
What is a good scanner that shows freeze frames and live data for us diy guys to diagnose these readings without breaking the bank?
friend just had the issue turns out Brake booster was rusted and allowing air in, Pinching the vacuum line to the booster proved the issue at the booster was the cause
could a code still be stored after torn air intake boot was replaced?
P0171
I would like to add something to this that i just experienced. I have the n249 delete sia delet etc. And this code gave me the run around for weeks. Smoke test leak test everything. Well because of those deletes i have bypassed my diverter vacuum line to the throttle body next to bank 1. Well the vacuum side of the diverter when out and was allowing boost pressure to enter after the trottle body right into bank 1. Long story short. New diverter valve fixed it. Sad part about this is a smoke test wont show it
Can a engine with a skip in cylinder 4 cause a code of p2098 thanks
My A/F ratio is showing 18-20 Air fuel ratio. Its a single turbo fresh build Infiniti G35. You think I can just bring it for tuner to adjust it? Fresh built engine.
Hay bud i just replaced my upstream & my downstream o2seners & replaced all my seners on the engine now im getting a p0171 code plz help
Excellent review, very informative and detailed. Great display of knowledge.
What about a system lean during a specific condition? Like at idle? Would that be considered a vacuum leak/excessive air, or would we go more into fuel delivery? Or O2 sensor?
short answer... YES it could be either of those things
I had 2 codes on my Audi A4 Sedan B8 1.8TSI p2293 and p0243 I did change the high pressure feul pump and turbo Solenoid all codes gone but now having new code P0171 any advice the car drive but not 100% full power any advice please
When you said that O2 sensor TYPICALLY but not ALWAYS peg out at max LEAN signal, I'm fairly certain it's based on your own personal experiences exclusively, and not influenced by what you have heard from others...
My question is, how much of that supporting experience comes from ONLY V.W. / Audi ??? My gut tells me better than 75% stems solely from VW. Only reason I even bring this up at all is because based on my experience at independent shops where I have worked on just about ANY make and model of car in existence, it's a fairly even 50/50 split for O2 sensors to peg out either lean or rich when it kicks the bucket. I have yet to really find any rhyme or reason as to the causes of either death result... I feel a SLIGHT bias of Rich codes in American vehicle like Ford and GM. It may not even be real and if it is real, it's very very slight...
Hey, I have a question. Is it possible that Longtube headers and no catalytics on my 1999 Mustang GT are causing a lean condition? Ive changed alot to stock as i bought it modded. Only thing aftermarket is those headers. Also I will have the PCM Reflashed at ford to the stock flash in case the tuner I used didnt do the job right, just to start with a clean slate. Revving the engine repeatedly makes the fuel trims go down from 25% to 10-17% idling until I leave it idle too long then they rise again.
Hey Charles, great video by the way.
Broda i have a misfire that starts when the engine is at working temp.
After i downshift at aceleration. Mostly at 2nd and 3rd gear.
Spark plugs are new, cables as well. ( its a Seat leon 1.4 16v axp engine 2002).
The fuel pump resistance gives me 3.5 ohms. According to the info i have seen that it should not be over 3 ohms. So im starting to think that is the fuel pump that when it gets hot dosent reach the minimun pressure. And the mixture gets lean.
What do you think or what would you do for this case.
Thanks a lot, and sorry to disturb.
God bless you.
So how much for the air intake?
Man so much good information, great video. Quick question, they did a fuel decarbonation and fuel duct cleaning and my car is back firing at idle and acceleration, is that normal for the first few days?
Mr. HumbleMechanic would i still have a p0171 if my K&N air filter was slighlty torn a size of a penny? My fuel pump/filter was replaced 15kmiles ago.
It’s possible. Air filter issues can disrupt airflow into the engine. But it’s very dependent on the engine
very cool charles TIL thanks for the awesome vods
I have saturn ion i put a short ram intake in but there is a secondary air injection hose out and i get a check egine light idk to replace it back to stock or try n remove the hose
I replaced the O2 sensor because a mechanic told me to replace it. Did not fix the problem. Is replacing the 02 sensor first the best choice. The scanner said running lean Bank 1.
Martin Albert did you ever fix the problem ?
What could cause P2188 (too rich at idle) without having any symptomps? (caxa engine)