EVAP codes in 2000 Corolla and two different mechanics can't figure it out

toyota
corolla

#1

My 2000 Corolla VE had a check engine light come on a couple months ago, so I took it to my trusted mechanic. He said the VSV valve was shorted out and replaced it. A couple days later, the check engine light came on again so we took it back. They said the initial VSV failure caused gasoline to get into the charcoal canister, and we needed a new canister. He said they should have caught it the first time, so he only charged me for the part and not the labor (he’s a nice guy!). Well, a couple days later, the check engine light came on again. So back we went, and they looked at the car again. But this time nothing seemed to be wrong. They double checked everything, basically threw up their hands and said to take the car to a dealer.

Well, I had a bad bad experience with our local Toyota dealership shop, so I took my car to another friend mechanic who specializes in Toyotas. He checked and rechecked the entire system, and can’t find anything wrong with anything. They checked for leaks/cracks/kinks in the hoses, checked the valves and canister. Nothing out of order. Everything tests fine. They threw up their hands too and can’t figure this thing out. I need new registration tabs at the end of this month and I’m nervous that the car won’t pass with evap codes. I don’t know what to do. Any ideas?



p.s. the gas cap was also replaced after visit #2, when they replaced the canister.



Also, when I fill up with gasoline, I never ever ‘top off’ the tank.



Help.


#2

One thing I don’t see mentioned is testing of the vapor pressure sensor. Also alldata mentions pulling the freeze frame data associated with the code to see if any of the collateral conditions are helpful in diagnosis.

If everything is working, the tank will build pressure with the purge valve closed; the tank shows reducing vapor pressure when the purge valve and VSV pressure switching valve are open; and the canister shows reducing when the purge valve is open and VSV pressure switching valve is closed, then you might have to look at the ECM. You might hunt down another dealership you can trust because there seems to be a special evap test tools that they may have (saw a TSB).

Anyway, when you solve this problem, let us know what the solution was.


#3

Testing for an evap system code can be very difficult. Make, model and year specific issues can complicate the diagnosis. A regulated nitrogen tank and necessary hardware to connect it to the car and the proper procedure to systematically trigger the correct sequence of valve openings and closings while monitoring the pressures and sniffing for leaks is time consuming and often best left to dealers with mechanics familiar with the car. There are some vary good dealers out there. Good luck.


#4

I forgot to add that the car has been hesitating from a cold start…then after a couple minutes it’s fine. My husband has been driving this car lately and failed to mention this fact. (GRRRR) Do you guys think the hesitation and evap codes are related?


#5

How smoothly does the engine idle and at what RPM? An intake leak or miss-connected vacuum lines could cause both problems.


#6

The car does not have an RPM gauge on the dash, and I haven’t noticed any rough idling. But then again, I haven’t driven it much in the last couple months. I’ll have to take it for a drive when my husband gets home from work.


#7

One situation that might cause this is if the purge VSV is constantly ‘on’ or commanded ‘on’ at the wrong time. Usually canister purge is not started until the vehicle is warmed up and in closed loop, cruise mode. If the purge valve is stuck open or the ECM is erroniously commanding purging, this could well cause a cold lean condition evinced by a hesitation.

As a test (only) you could disconnect the purge valve and see if the hesitation abates.

Hope this points you in the right direction.


#8

Evap codes certainly are harder to figure out than some other systems.