Tracking a EVAP leak and need someone with more knowledge than I. I understand that generally in the Camry I4s I have had (and my 2008 4Runner v6) there are two VSV units, one in the engine bay that opens to allow EVAP gasses from the tank and canister in to the intake during engine operation (the purge VSV, Normally closed),and a vent VSV (normally open?) that opens and closes the vent of the Canister to the outside air for gases that have gone through the charcoal medium. After some period of engine off time (5 hours ish) the EVAP check cycle will run during which both VSVs will be closed and a vacuum formed in the system. The ECM then compares any drop in vacuum over a long watch period to its calibration vacuum drop. If it is a "small leak" is will throw a P0456. If it is a 'large leak" it will throw a P0455 and/or a P0441.
Leaks may be caused by any of the following:
1) faulty VSV (purge or vent) - either fail to open/close or just leak (more likely as it cycles thousands of times).
2) rotten/holed flex line or bad clamp either near the purge or the vent VSV/Canister (less likely damaged steel line)
3) crack in the Canister
4) faulty gas overfill line
5) bad or missing gas cap seal. (can be a simple fix for P0456 code)
6) Another leak in the gas tank like the seal of the fuel pump etc. (tough to diagnose and less likely)
7) Bad ECM (I like to think this is least likely)
Am I missing anything?
In my case, my 2008 4Runner V6 threw a P0456 first. I cleaned the gas cap gasket and checked the flex lines in the engine bay, finding some cracking in a line near the exhaust. I checked the lines with a vacuum pump and trimmed the faulty line until I had a clean and non cracked connection. I cleared the MIL with my scanner and the next morning MIL was back, this time throwing P0455, P0456,a nd P0441
I then tested the Purge VSV. I put a vacuum on the manifold side of the purge VSV with the power off (this VSV should be a default closed switch) and it held a steady 25 inches Hg. I then tested the side of the same valve that went to the tank. It would not take more than 15 inches Hg and rapidly dropped to less than 10 inches every time. I have not yet gotten under the truck to see how the canister and vent VSV hold a vacuum.
I assumed at this point the purge VSV was bad for not holding vacuum. On a whim I pulled the purge VSV (a slightly different style) off my 2012 Camry I4 and oddly, it exhibited the same behavior – it holds as much vacuum as I can give it from the manifold side but only a max of about 15 inches on the tank side and it drops, but it has many fewer miles and has never thrown an EVAP code.
Help. I have also asked this on the ToyotaNation forum as it is not 4Runner exclusive.
Jeff-in-KC
Leaks may be caused by any of the following:
1) faulty VSV (purge or vent) - either fail to open/close or just leak (more likely as it cycles thousands of times).
2) rotten/holed flex line or bad clamp either near the purge or the vent VSV/Canister (less likely damaged steel line)
3) crack in the Canister
4) faulty gas overfill line
5) bad or missing gas cap seal. (can be a simple fix for P0456 code)
6) Another leak in the gas tank like the seal of the fuel pump etc. (tough to diagnose and less likely)
7) Bad ECM (I like to think this is least likely)
Am I missing anything?
In my case, my 2008 4Runner V6 threw a P0456 first. I cleaned the gas cap gasket and checked the flex lines in the engine bay, finding some cracking in a line near the exhaust. I checked the lines with a vacuum pump and trimmed the faulty line until I had a clean and non cracked connection. I cleared the MIL with my scanner and the next morning MIL was back, this time throwing P0455, P0456,a nd P0441
I then tested the Purge VSV. I put a vacuum on the manifold side of the purge VSV with the power off (this VSV should be a default closed switch) and it held a steady 25 inches Hg. I then tested the side of the same valve that went to the tank. It would not take more than 15 inches Hg and rapidly dropped to less than 10 inches every time. I have not yet gotten under the truck to see how the canister and vent VSV hold a vacuum.
I assumed at this point the purge VSV was bad for not holding vacuum. On a whim I pulled the purge VSV (a slightly different style) off my 2012 Camry I4 and oddly, it exhibited the same behavior – it holds as much vacuum as I can give it from the manifold side but only a max of about 15 inches on the tank side and it drops, but it has many fewer miles and has never thrown an EVAP code.
Help. I have also asked this on the ToyotaNation forum as it is not 4Runner exclusive.
Jeff-in-KC
