Yours is the absolute best EVAP tutorial and I've spend a ton of time researching. And your video is perfect since I'm troubleshooting a 2002 Toyota Sienna that uses the EVAP system you describe. Thank you for posting your youtube video.
This is absolutely the single best, concise, clear explanation of any automotive system that I have ever seen. Just absolutely fantastic. I would subscribe to any paid training courses that you developed going forward. Brilliant!!!
wow that is by far the best toyota evap complete analysis and diagnostic video on the market. byron you certainly did the homework and nailed it. scoping your own pressure was awesome. i like the visuals of the canister and diaphams. thanks for taking the mystery out of the system. God bless you for making this video. You really showed you excellence.
Tremendous video. I have one these Toyota’s at work with a P0442 and this video helped me immensely. The key is the bypass valve and splitting it into two separate systems. Again, fantastic video and thanks!
Thanks for this very indepth video. I've been looking for an indepth video on evap systems and this is the only one i've found that answers my questions. I've been chasing the p0442 on a 98 Ford F150 5.4 liter and this video just made it easier for me.
Just came across this, excellent description. Techstream, which is the Toyota factory tool, only lets us close the vent valve for 10 seconds also. The key is there is 3 valves and, essentially, 2 vent openings. You have to clamp off that other vent line when smoke testing these.
Thank you for this video. On my 2000 Camry I am having P0440, P0441 and P0446. I already replaced the charcoal cannister with a brand new one but its a Dorman unit and still getting the codes come back. I also replaced the valve that is attached to the air cleaner box as it was bad before. I crimped off the hose with the yellow linee on it and smoke tested it from the engine bay to the tank and do not see any smoke at all. At my wits end. Don't want to spend the money for a Toyota unit and that not be the problem. I do notice a slight hiss somewhere above the tank if I put enough pressure into the evap line ( I was doing it by mouth ) at the engine.
This is the best instructional video, better than some of the GM and others instructions. I work on testing of the CVS as a tier one supplier and have read many poorly written Engineering Specifications. I am helping a Lady Friend to fix her Toyota error codes. Thank You for the clearly stated help.
Was watching another video about Toyota EVAP systems, and they mentioned a valve that is on top of the fuel tank, NOT where the fuel pump and fuel lines exit the tank but an actual valve that inserts into the tank. You didn't mention it in your video. Is this something in "older" Toyota systems? If so, is it something that went away after a certain year? I did notice this video is from 2014. How can we tell if our vehicle has this valve on the tank without dropping the gas tank or cutting a hole in the floorboard?
Great video.. 02 tacoma with a 0440 that won’t go away after replacing a leaky fuel neck. I tried smoke testing again but it feels like the line is blocked? Any ideas thanks
I did this with an engine vacuum gauge ($25 at my local auto parts store) by connecting it to the EVAP service port. I had to remove the valve core (using needle nose pliers) from the EVAP service port. The valve core was LEFT HAND THREADED on my 2004 Corolla. This process detected the leak just like the video shows.
Mine is a 2003 4 cyl Camry that seems to now be super sensitive to a P0442 ever since I put an oem fuel cap on it. I had an aftermarket cap that started to have bad ratcheting upon tightening so I bought an oem. It had never set the code before. I swear, if I don't ratchet it 3x the light will come on. Perhaps the cap is defective.
Brian, Excellent Video, i kept this video as bible .. i re-watched this again after 2 years, hope you can answer me. Please. at 1) 8.19 in your video timeline you said, 9 out of 10 times it is canister seals , in case if that seal is going bad, will the smoke machine show the leaks. 2) to pressure test you asked me to crimp the yellow band hose, what is maximum PSI i can put less than aPSI. 3) if i block vent valve and assuming my normally closed bypass valve is closed and if the vaccum is holding well by opening purge control valve. can i assume canister is good?? 4) if step 3 is good, and to test fill valve, gas tank, i need to put pressure, i use hand mityvac pump to put pressure, when i put pressure how do i know if overfill valve is a problem, or fuel filler neck is the problem. 5) can i put smoke with .5 psi on bypass valve side of thehose that goes to the tank and watch FTP raising in scann tool and it maintain that pressure. i dont know step 4 diaagnosis, rest all i am good. please advise..
Hi, I hope you still available 👋. With regards to the diaphragms in those two barrel shape plastic Solenoid in both sides. First Q, goes to the one on the left, the one under the FPS, it has on very top a venting outlet with a small rubber tube shaped (L) hiding at the lateral and back side of this plastic Solenoid piece. Is it blocked if I apply pressure inside this specific orifice, and the air doesn't pass, the air has no way to scape because the top of the diaphragm inside either normally tightly sealing the air passage or stuck in ? It seems a one way vent? Because by utter chance, I tested the next to it, same look a like piece, which is on the right side near the drain hose. This part has a very short tube in the lower or bottom connected to the Air inlet tube, I removed the tube on the side of this barrel shape piece and pushed air inside, to my surprise the air didn't pass, exactly like what happened to the resisting diaphragm on the left component! I think it is one way exit, but then what its function? Please if you have time, let me know, I really don't want to buy a new canoes on guessing. By the way, the canister itself looks very good and passes all the basic air circulation, no clogging. Thanks 🙏🙏🙏
Well done sir. Question: 2003 Corolla EVAP canister, there are 3 diaphragms. One of mine does not hold a vacuum. I thought bad canister and when cut open I found a tear in it. So, a Toyota canister from Amazon showed the same issue. Note: I opted for a returned item, retaped, but looked uninstalled. I wish I could test another. Any ideas?
great video thank for sharing a question where were you tapped into canister side of system exactly? did you have adapter to tap in with your WPS500? thanks mark ferraro
Hi Mark. There is a green evap port designed to check evap pressure. It's located on the evap vent line. You have to remove the valve stem and connect an adapter (looks like a GM fuel pressure tester). My WPS500 connects to the evap adapter.
Very nice explanation and presentation Byron. One question though. Where do you have your pico scope pressure sensor tapped into the system when you are performing the canister side of the system? In the schematic you show the VP sensor in the tank side, not the canister side. Or am I reading it wrong?
Thank you Andrew. The evap test port will usually have a green cap and is located close to the air filter. That is where I have the pressure transducer located. The 'vapor pressure sensor' is physically located on the charcoal canister, but piping connects it directly to fuel tank. Only the PCM or scan tool can read the 'vapor pressure sensor'. The pressure reading I show in the video is from the WPS500 pressure transducer using pico scope software.
Bryon Smith Thanks Byron for your reply. That makes sense but you didn't mention your connection location in your video. As a professional auto tech myself I find Toyota Evap diagnosis one of the more challenging due to the terminology that can be confusing. So using your procedure, monitoring system pressure (vacuum) via the service port, with the VSV closed, CCV closed and purge VSV PWM open, then closed ONLY the Canister side of the system is monitered. Correct?
Hi there, thank you so much for your detailed video. I am watching this for a second time but i thought I would add a question while I am watching. I do have a p0440, p0441, and p0446 , not p0442 on my 02 4runner. some signs my venting is not working is when i go pump at the gas it keeps stopping mid way between. This is intermediate as sometimes it does it flawlessly. Next what I have also notice once that when I took off the gas cap to make sure it was seated properly I heard a rush of air meaning it was holding vacuum. At least, So far this leads me conclude there is no leak from gas tank side of the pressure switching. however I don't know where else that leave me. Any clues? Thanks.
Hi Bardia, The venting problem could be a restriction in the vent tube or defective charcoal canister. Look for dirt in the vent tube coming from the charcoal canister. The code p0441 is a low/no flow purge solenoid. If it's intermittent then check the connections to the purge solenoid or fuel pressure sensor. Unplug them and look for corrosion (green growth on the metal contacts). When you plug back in, make sure connector seats well. Hope it helps. Bryon
+Bryon Smith Hi Bryon, Thanks for the quick reply. The vent tube connects the charcoal canister to the gas tank? What could cause an obstruction? All the lines are rusted, maybe it collapsed on itself? and im scared to touch. I know the canister comes with new flexible lines, but i think when i try to connect them to hard lines, the hard lines will fall apart. Thank again
Yes you are correct. What ever breaks while changing/testing the evap canister has to be replaced. Welcome to the life of a Technician! Find a good used/wrecked vehicle to get parts from if they break.
correct me if I am wrong, the color graph you are showing air flowing from the air cleaner to the charcoal canister direction is that correct? air shuld be moving in the directon to the air cleaner as the vaccum sorce is very stong right?
The throttle plate is the divide between engine vacuum and atmosphere. The air filter is only under vacuum when the throttle plate is fully open and then it is very, very minor. The evap doesn't run when throttle is wide open. The air filter is designed to flow as much air as the engine can consume + some (to account for dirt over time - typically 30,000 miles worth of filtering).
QUESTION. Scan data provides a % Commanded Purge, which I gather is related to the vacuum in the intake manifold. Usually then higher engine load greater commanded purge. Though that doesn't always seem to be the case in the data, though it must be, as the purge valve is either open or closed, not having graduated positions. The Question is does the ECM actually know the amount of fuel vapor coming in a purge, or does it just guess using preset tables? Does the ECM know the level of depletion of the Canister? Say a long purge at 100% will deplete the reserves of the canister faster than it can be replaced. Does the ECM know this, or rely on 02 sensors to adjust Fuel Trim? This question relates to assessing the cause of high fuel trims at higher loads. IF the ECM is assuming fuel delivery rather than actually knowing the fuel delivery from the canister, then a degraded/inefficient canister can be the cause of higher fuel trims. Im not referring to leaks but degraded charcoal etc. Commanded purges should remain constant over time I gather, being related to vacuum pressures? THUS it would be nice if there were a sensor that recorded the % of fuel vapor being delivered at a certain % purge. You could then compare the specs of your new car against a few years later and know if an increased Long Term Fuel Trim was related to the Evap system purge or not. I have seen a Patent where there was a calculation of fuel vapor being delivered in a purge, but am not aware if this is included in cars now days.
Purge Valve Operation The ECM monitors the throttle position sensor, engine load, o2 sensors and a few others. When all conditions are met, it opens the purge valve. The purge valve is pulse width modulated. Meaning it cycles off/on many times a second. This design allows the ECM to vary it's duty cycle and change the flow amount, not just off or on. (Think of squeezing a drinking straw to reduce flow then slowly letting go.) Evap Canister Purge Operation The ECM only responds to inputs from the various sensors, the main one being the o2 sensor. The sensor only monitors oxygen in the exhaust stream, so excessive oxygen = lean, no oxygen = rich. Vehicles do not have hydrocarbon (raw fuel) sensors. As hydrocarbons enter the intake through the purge valve, the o2 sensor will 'see' oxygen level is dropping and it will reduce the pulse width timing on the injectors to reduce fuel amount. The ECM is trying to maintain stoichiometric (14.7 air molecules to 1 fuel molecule) under all operating conditions, no matter if the purge is open or not. Purpose of Evap Canister To prevent hydrocarbons from getting into the atmosphere and allow air to vent from fuel tank as it is being refueled. The hydrocarbons 'stick' to the charcoal inside the canister. Hence the name, charcoal canister. There is no good/bad charcoal. The way it fails is by leaking or becoming plugged up. Evap Canister Monitoring There is no need to monitor the amount of fuel passing through the purge valve. The oxygen sensors report if more or less fuel is needed to remain stoichiometric. If your fuel trims are off, and your wondering if the purge valve is causing the problem, then clear out short term memory, disable purge by unplugging it, and see if the problem with the fuel trims go away. It's rare, but I've seen people fill the cars with fuel to the top of the fuel neck, then fuel trims will be unusually high till the fuel level drops. The car will still maintain stoichiometric, so fuel mileage will not change, just fuel trims as the computer adjust to the extra fuel entering the engine through the purge valve.
Hello TAQ. Would you help me solve a evap problem with my 1999 toyota please. It is a 2.2L engine. I've been getting the P0441 and P0446 MIL codes. I replaced the purge solenoid valve that's in the engine compartment next to the air cleaner. That didn't help. I cleared the codes and they came right back. I also tested the old purge valve with a 12 VDC power supply and it does open and close - so I guess that was a learning experience that didn't help. I then changed the valve that is mounted to the charcoal canister, then reset the codes. They came right back again. I also tested that valve that I took off - and tested okay. I bought the entire charcoal canister assembly from a Toyota dealer. I got it cheaper shopping an internet dealer and it came brand new in the Toyota box. I looked at the old canister and realized I couldn't figure out how to remove it, so I took the new part and car to the dealer near me and they changed it for me. I cleared the codes again and went for a drive. After my second trip, the MIL came on again - this time only the P0441 error. I'm not sure what else I can do to fix this problem. I need to get the car smogged in two weeks or I'll run late on my registration renewal. I'd sure appreciate some help if you have the time. One more thing: I saw a hose that goes from the intake box down under the car - it changes from a rubber hose to steel tube and I think it goes to the carbon canister. I don't see a valve for this air supply. If there is one, do you know where it is? If I understand P0441 correctly, it is telling me that there is no flow when the purge should be occurring. What could cause this that I haven't already changed? Thank you. Dale
Frazzled Update: I checked the hose that goes from the intake box down under the car. I thought that could be the air intake for the carbon canister, but it's not functional (and never was) The intake box has the fitting for the hose but the hole is plugged because the hole was never opened into the airbox. Maybe this is for a different version of 99 camry?
Pico software and WPS500 can be purchased through Autonerdz.com. There a few dollars more expensive, but it comes with the most amazing training that can't be found anywhere else. Tom's team of experts are great people.
2nd comment- At 14:05 you were testing the canister side of the system ( with bypass valve closed) and you saw vaccum decay which you determined that either the system has a hole in the tubing/hoses or the canister is bad. I think you forgot one thing. If the bypass valve is leaking then wont you see a similar decay in vaccum? With a bad bypass valve you are now checking the entire system because the bad bypass valve didn't properly isolate the system. What say you?
You could be right, but nobody is going to pay me for the extra time to find out. Most of the parts on the charcoal canister are not replaceable, so the whole canister gets replaced which includes the bypass valve. The only way to verify the leak is to take the charcoal canister apart and test pieces individually. I've tested many of them and the most common leak is in the vacuum pods, but could be other things as well.
At 11:58 your graph shows 14.7psi = 29.92 inHg. Doesn't 14.7 psi actually equal 0 inHg? And 0 psi equals 29.9 inHg? Or am I missing something. Otherwise, good video, thanks.
Your confusing gauge pressure with absolute pressure. Gauge pressure is what mechanics gauges are calibrated to, 0 psi gauge reading is actually 14.7 psi absolute at sea level. I am using gauge pressure in the video.
The best I've seen that explain how the evap system operation and how to do the unit test.
Yours is the absolute best EVAP tutorial and I've spend a ton of time researching. And your video is perfect since I'm troubleshooting a 2002 Toyota Sienna that uses the EVAP system you describe. Thank you for posting your youtube video.
This is absolutely the single best, concise, clear explanation of any automotive system that I have ever seen. Just absolutely fantastic. I would subscribe to any paid training courses that you developed going forward. Brilliant!!!
Very helpful. It is hard to find someone who explains the system this well. Thank you.
Greatest EVAP tutorial I’ve ever seen thank you
wow that is by far the best toyota evap complete analysis and diagnostic video on the market. byron you certainly did the homework and nailed it. scoping your own pressure was awesome. i like the visuals of the canister and diaphams. thanks for taking the mystery out of the system. God bless you for making this video. You really showed you excellence.
opps your excellence
Tremendous video. I have one these Toyota’s at work with a P0442 and this video helped me immensely. The key is the bypass valve and splitting it into two separate systems. Again, fantastic video and thanks!
Wow Man U just nailed like true engineering wow great content keep producing good content
Thanks. I wish I’d seen this video earlier. I appreciate you making this video. It truly is very helpful in understanding evap systems.
Thanks for this very indepth video. I've been looking for an indepth video on evap systems and this is the only one i've found that answers my questions. I've been chasing the p0442 on a 98 Ford F150 5.4 liter and this video just made it easier for me.
Excellent explanation of the Toyota EVAP system . Thank you very much
Excellent tutorial sir. I really appreciate your time explaining Toyota EVAP system. Cheers👍
Awesome thanks for everything you do
Awesome video :) Thank you for putting in the time
this is a great video! thank you so much.
Just came across this, excellent description. Techstream, which is the Toyota factory tool, only lets us close the vent valve for 10 seconds also. The key is there is 3 valves and, essentially, 2 vent openings. You have to clamp off that other vent line when smoke testing these.
Thanks for your great job and share your knowledge and experience.
Thank you so much!!! Omfg!!
This is an awesome video!!
great job! very good video
very very awesome video thanks for uploading
Thank you for this video. On my 2000 Camry I am having P0440, P0441 and P0446. I already replaced the charcoal cannister with a brand new one but its a Dorman unit and still getting the codes come back. I also replaced the valve that is attached to the air cleaner box as it was bad before. I crimped off the hose with the yellow linee on it and smoke tested it from the engine bay to the tank and do not see any smoke at all. At my wits end. Don't want to spend the money for a Toyota unit and that not be the problem.
I do notice a slight hiss somewhere above the tank if I put enough pressure into the evap line ( I was doing it by mouth ) at the engine.
best explantion on evaps thank you very much it was very helpfull
This is a good instructional video. Thanks alot.
This is the best instructional video, better than some of the GM and others instructions.
I work on testing of the CVS as a tier one supplier and have read many poorly written Engineering Specifications.
I am helping a Lady Friend to fix her Toyota error codes. Thank You for the clearly stated help.
Thank you very much Dan.
very nice video , thanks for sharing
Excellent explanation of what system. Thank you very much for sharing.
Amazing video!,,,, I lije this bideo!,,
Was watching another video about Toyota EVAP systems, and they mentioned a valve that is on top of the fuel tank, NOT where the fuel pump and fuel lines exit the tank but an actual valve that inserts into the tank. You didn't mention it in your video. Is this something in "older" Toyota systems? If so, is it something that went away after a certain year? I did notice this video is from 2014. How can we tell if our vehicle has this valve on the tank without dropping the gas tank or cutting a hole in the floorboard?
Great Video, now I hope I can figure out why my 2003 Corolla keeps getting those codes even after replacing the fuel cap with an OEM cap.
Great video.. 02 tacoma with a 0440 that won’t go away after replacing a leaky fuel neck. I tried smoke testing again but it feels like the line is blocked? Any ideas thanks
I did this with an engine vacuum gauge ($25 at my local auto parts store) by connecting it to the EVAP service port. I had to remove the valve core (using needle nose pliers) from the EVAP service port. The valve core was LEFT HAND THREADED on my 2004 Corolla. This process detected the leak just like the video shows.
I just found this video lol how are you getting a reading showing a leak from the canister when the pressure sensor is sealed off with the tank?
which scan tool do you use to measure the vapor pressure sensor? thanks
Do you connect the vacuum transducer to the evap test port?
Mine is a 2003 4 cyl Camry that seems to now be super sensitive to a P0442 ever since I put an oem fuel cap on it. I had an aftermarket cap that started to have bad ratcheting upon tightening so I bought an oem. It had never set the code before. I swear, if I don't ratchet it 3x the light will come on. Perhaps the cap is defective.
2002 4runner 3.4 same codes check engine vsc off vsc trac lights on. Would this apply to the vsc lights also?
Brian, Excellent Video, i kept this video as bible .. i re-watched this again after 2 years, hope you can answer me. Please.
at 1) 8.19 in your video timeline you said, 9 out of 10 times it is canister seals , in case if that seal is going bad, will the smoke machine show the leaks.
2) to pressure test you asked me to crimp the yellow band hose, what is maximum PSI i can put less than aPSI.
3) if i block vent valve and assuming my normally closed bypass valve is closed and if the vaccum is holding well by opening purge control valve. can i assume canister is good??
4) if step 3 is good, and to test fill valve, gas tank, i need to put pressure, i use hand mityvac pump to put pressure, when i put pressure how do i know if overfill valve is a problem, or fuel filler neck is the problem.
5) can i put smoke with .5 psi on bypass valve side of thehose that goes to the tank and watch FTP raising in scann tool and it maintain that pressure.
i dont know step 4 diaagnosis, rest all i am good. please advise..
Hi, I hope you still available 👋.
With regards to the diaphragms in those two barrel shape plastic Solenoid in both sides.
First Q, goes to the one on the left, the one under the FPS, it has on very top a venting outlet with a small rubber tube shaped (L) hiding at the lateral and back side of this plastic Solenoid piece. Is it blocked if I apply pressure inside this specific orifice, and the air doesn't pass, the air has no way to scape because the top of the diaphragm inside either normally tightly sealing the air passage or stuck in ? It seems a one way vent? Because by utter chance, I tested the next to it, same look a like piece, which is on the right side near the drain hose. This part has a very short tube in the lower or bottom connected to the Air inlet tube, I removed the tube on the side of this barrel shape piece and pushed air inside, to my surprise the air didn't pass, exactly like what happened to the resisting diaphragm on the left component!
I think it is one way exit, but then what its function?
Please if you have time, let me know, I really don't want to buy a new canoes on guessing.
By the way, the canister itself looks very good and passes all the basic air circulation, no clogging.
Thanks 🙏🙏🙏
I saw the part where u said when your pumping gas and it stops itself its a vent issue? what exactly should I check?
very nice
Well done sir. Question: 2003 Corolla EVAP canister, there are 3 diaphragms. One of mine does not hold a vacuum. I thought bad canister and when cut open I found a tear in it. So, a Toyota canister from Amazon showed the same issue. Note: I opted for a returned item, retaped, but looked uninstalled. I wish I could test another. Any ideas?
What does too much vacuum on system during self check mean ?
great video thank for sharing a question where were you tapped into canister side of system exactly? did you have adapter to tap in with your WPS500? thanks mark ferraro
Hi Mark. There is a green evap port designed to check evap pressure. It's located on the evap vent line. You have to remove the valve stem and connect an adapter (looks like a GM fuel pressure tester). My WPS500 connects to the evap adapter.
Very nice explanation and presentation Byron. One question though. Where do you have your pico scope pressure sensor tapped into the system when you are performing the canister side of the system? In the schematic you show the VP sensor in the tank side, not the canister side. Or am I reading it wrong?
Thank you Andrew. The evap test port will usually have a green cap and is located close to the air filter. That is where I have the pressure transducer located. The 'vapor pressure sensor' is physically located on the charcoal canister, but piping connects it directly to fuel tank. Only the PCM or scan tool can read the 'vapor pressure sensor'. The pressure reading I show in the video is from the WPS500 pressure transducer using pico scope software.
Bryon Smith
Thanks Byron for your reply. That makes sense but you didn't mention your connection location in your video. As a professional auto tech myself I find Toyota Evap diagnosis one of the more challenging due to the terminology that can be confusing. So using your procedure, monitoring system pressure (vacuum) via the service port, with the VSV closed, CCV closed and purge VSV PWM open, then closed ONLY the Canister side of the system is monitered. Correct?
Hi there,
thank you so much for your detailed video. I am watching this for a second time but i thought I would add a question while I am watching.
I do have a p0440, p0441, and p0446 , not p0442 on my 02 4runner.
some signs my venting is not working is when i go pump at the gas it keeps stopping mid way between. This is intermediate as sometimes it does it flawlessly.
Next what I have also notice once that when I took off the gas cap to make sure it was seated properly I heard a rush of air meaning it was holding vacuum. At least, So far this leads me conclude there is no leak from gas tank side of the pressure switching. however I don't know where else that leave me.
Any clues?
Thanks.
Hi Bardia,
The venting problem could be a restriction in the vent tube or defective charcoal canister. Look for dirt in the vent tube coming from the charcoal canister. The code p0441 is a low/no flow purge solenoid. If it's intermittent then check the connections to the purge solenoid or fuel pressure sensor. Unplug them and look for corrosion (green growth on the metal contacts). When you plug back in, make sure connector seats well.
Hope it helps.
Bryon
+Bryon Smith Hi Bryon, Thanks for the quick reply. The vent tube connects the charcoal canister to the gas tank? What could cause an obstruction? All the lines are rusted, maybe it collapsed on itself? and im scared to touch. I know the canister comes with new flexible lines, but i think when i try to connect them to hard lines, the hard lines will fall apart.
Thank again
Yes you are correct. What ever breaks while changing/testing the evap canister has to be replaced. Welcome to the life of a Technician! Find a good used/wrecked vehicle to get parts from if they break.
Thanks a lot for great instructional video, just a quick question: where did you connect your Pico scope leads to, which component, thanks again
My pico is connected to the WPS500 pressure transducer. I am manually activating the evap solenoids with jumper wires.
correct me if I am wrong, the color graph you are showing air flowing from the air cleaner to the charcoal canister direction is that correct? air shuld be moving in the directon to the air cleaner as the vaccum sorce is very stong right?
The throttle plate is the divide between engine vacuum and atmosphere. The air filter is only under vacuum when the throttle plate is fully open and then it is very, very minor. The evap doesn't run when throttle is wide open. The air filter is designed to flow as much air as the engine can consume + some (to account for dirt over time - typically 30,000 miles worth of filtering).
QUESTION. Scan data provides a % Commanded Purge, which I gather is related to the vacuum in the intake manifold. Usually then higher engine load greater commanded purge. Though that doesn't always seem to be the case in the data, though it must be, as the purge valve is either open or closed, not having graduated positions. The Question is does the ECM actually know the amount of fuel vapor coming in a purge, or does it just guess using preset tables? Does the ECM know the level of depletion of the Canister? Say a long purge at 100% will deplete the reserves of the canister faster than it can be replaced. Does the ECM know this, or rely on 02 sensors to adjust Fuel Trim? This question relates to assessing the cause of high fuel trims at higher loads. IF the ECM is assuming fuel delivery rather than actually knowing the fuel delivery from the canister, then a degraded/inefficient canister can be the cause of higher fuel trims. Im not referring to leaks but degraded charcoal etc. Commanded purges should remain constant over time I gather, being related to vacuum pressures? THUS it would be nice if there were a sensor that recorded the % of fuel vapor being delivered at a certain % purge. You could then compare the specs of your new car against a few years later and know if an increased Long Term Fuel Trim was related to the Evap system purge or not. I have seen a Patent where there was a calculation of fuel vapor being delivered in a purge, but am not aware if this is included in cars now days.
Purge Valve Operation
The ECM monitors the throttle position sensor, engine load, o2 sensors and a few others. When all conditions are met, it opens the purge valve. The purge valve is pulse width modulated. Meaning it cycles off/on many times a second. This design allows the ECM to vary it's duty cycle and change the flow amount, not just off or on. (Think of squeezing a drinking straw to reduce flow then slowly letting go.)
Evap Canister Purge Operation
The ECM only responds to inputs from the various sensors, the main one being the o2 sensor. The sensor only monitors oxygen in the exhaust stream, so excessive oxygen = lean, no oxygen = rich. Vehicles do not have hydrocarbon (raw fuel) sensors. As hydrocarbons enter the intake through the purge valve, the o2 sensor will 'see' oxygen level is dropping and it will reduce the pulse width timing on the injectors to reduce fuel amount. The ECM is trying to maintain stoichiometric (14.7 air molecules to 1 fuel molecule) under all operating conditions, no matter if the purge is open or not.
Purpose of Evap Canister
To prevent hydrocarbons from getting into the atmosphere and allow air to vent from fuel tank as it is being refueled. The hydrocarbons 'stick' to the charcoal inside the canister. Hence the name, charcoal canister. There is no good/bad charcoal. The way it fails is by leaking or becoming plugged up.
Evap Canister Monitoring
There is no need to monitor the amount of fuel passing through the purge valve. The oxygen sensors report if more or less fuel is needed to remain stoichiometric. If your fuel trims are off, and your wondering if the purge valve is causing the problem, then clear out short term memory, disable purge by unplugging it, and see if the problem with the fuel trims go away. It's rare, but I've seen people fill the cars with fuel to the top of the fuel neck, then fuel trims will be unusually high till the fuel level drops. The car will still maintain stoichiometric, so fuel mileage will not change, just fuel trims as the computer adjust to the extra fuel entering the engine through the purge valve.
What the computer check when Po442 is set?
Hello TAQ.
Would you help me solve a evap problem with my 1999 toyota please.
It is a 2.2L engine.
I've been getting the P0441 and P0446 MIL codes.
I replaced the purge solenoid valve that's in the engine compartment next to the air cleaner. That didn't help. I cleared the codes and they came right back. I also tested the old purge valve with a 12 VDC power supply and it does open and close - so I guess that was a learning experience that didn't help.
I then changed the valve that is mounted to the charcoal canister, then reset the codes. They came right back again. I also tested that valve that I took off - and tested okay.
I bought the entire charcoal canister assembly from a Toyota dealer. I got it cheaper shopping an internet dealer and it came brand new in the Toyota box. I looked at the old canister and realized I couldn't figure out how to remove it, so I took the new part and car to the dealer near me and they changed it for me.
I cleared the codes again and went for a drive. After my second trip, the MIL came on again - this time only the P0441 error.
I'm not sure what else I can do to fix this problem. I need to get the car smogged in two weeks or I'll run late on my registration renewal. I'd sure appreciate some help if you have the time.
One more thing: I saw a hose that goes from the intake box down under the car - it changes from a rubber hose to steel tube and I think it goes to the carbon canister. I don't see a valve for this air supply. If there is one, do you know where it is?
If I understand P0441 correctly, it is telling me that there is no flow when the purge should be occurring. What could cause this that I haven't already changed?
Thank you.
Dale
Frazzled Update: I checked the hose that goes from the intake box down under the car. I thought that could be the air intake for the carbon canister, but it's not functional (and never was) The intake box has the fitting for the hose but the hole is plugged because the hole was never opened into the airbox. Maybe this is for a different version of 99 camry?
Hi Frazzled. Sorry for the late reply. Your problem seems more complex then most. Did you get it fixed?
What software are you using and where can it be purchased? Thank you, Great video too.
Pico software and WPS500 can be purchased through Autonerdz.com. There a few dollars more expensive, but it comes with the most amazing training that can't be found anywhere else. Tom's team of experts are great people.
2nd comment- At 14:05 you were testing the canister side of the system ( with bypass valve closed) and you saw vaccum decay which you determined that either the system has a hole in the tubing/hoses or the canister is bad. I think you forgot one thing. If the bypass valve is leaking then wont you see a similar decay in vaccum? With a bad bypass valve you are now checking the entire system because the bad bypass valve didn't properly isolate the system. What say you?
You could be right, but nobody is going to pay me for the extra time to find out. Most of the parts on the charcoal canister are not replaceable, so the whole canister gets replaced which includes the bypass valve. The only way to verify the leak is to take the charcoal canister apart and test pieces individually. I've tested many of them and the most common leak is in the vacuum pods, but could be other things as well.
At 11:58 your graph shows 14.7psi = 29.92 inHg. Doesn't 14.7 psi actually equal 0 inHg? And 0 psi equals 29.9 inHg? Or am I missing something. Otherwise, good video, thanks.
Your confusing gauge pressure with absolute pressure. Gauge pressure is what mechanics gauges are calibrated to, 0 psi gauge reading is actually 14.7 psi absolute at sea level. I am using gauge pressure in the video.