Lexus Troubleshooting Questions? Ask a Lexus Expert
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Whenever you have the P0440 code combined with the 441 and 446 the later 2 codes are usually false codes due to the evap system not being able to hold the correct pressures. The P0440 code is a leak in the evap system. Without a evap pressure tester/smoke generator it is difficult to find these leaks. If you live in a high corrosion area it is possible that the tank bypass VSV on the charcoal canister could set these codes or an internal leak in the canister can also do this.
It is very difficult to do diagnostics on these evap systems without the proper equipment. I do not like recommending parts replacement to solve a problem either. The good thing is that corrosion or rusted out filler neck and lines can probably be ruled out. However check the filler neck for pitted surfaces where the gas cap seals onto the filler neck. Also replace the gas cap with a Toyota or Lexus gas cap not a cheap walmart cap. These are the quick things and cheap things to try first. Let me know how the filler neck looks.
Have you tried the gas cap yet and are all the hoses connected? Did the car have any recent work done?
If there are no external leaks you are probably looking at the canister assembly. The VSV on the canister is know to go bad also but normally does not set the 440 unless the canister leaks internally. I have seen some of the diaphragms leak.