Intermittent EVAP Control System Failure

[nepathfinder]

Hi,

I have a strange intermittent problem that has affected my 97 Pathfinder for a while now. About every month or two my service engine light will come on and stay on solid. When I read the OBDII code it says P0440, EVAP Control System Failure. I replaced the gas cap, but it did not help. I have taken the truck to two mechanics and have taken it to the Nissan dealer twice, but they can't find anything wrong. They checked all the values and the charcoal canister and did a pressure check for leaks and everything is fine. The only answer they can give is to tighten the gas cap more, which I'm very careful about doing so I don't think that's it.

Does anyone know what's going on here? Is the problem intermittent and that's why nobody can find it?

Your advice is appreciated.

Great forum.

Dalton

[s13sr20chris]

p0440 is evap sys small leakit could be a small leak or it could be a control sys problem

if the techs could not find a leak then you are prob looking at a bad vent control valve. that is very common. the vent control valve is the valve with two 10mm bolts bolting it to the charcoal canister. you can pull it off and test it. to test you blow air through it. should be easy. then apply 12v to the two terminals and try again. it should not go through at all. if that is not how it works then you need a vent control valve. most nissan dealers should have it in stock.

[nepathfinder]

Thanks for the advice. I will look into the vent control value. Do you know how often the EVAP system is tested? I'm wondering why I only get the check engine light every 1-2 months. if there was a real leak or a bad value, I'd think I'd have the light on a lot more often. Unless of course the value or control system only sometimes has a problem. Could the value get a little stuck only occationally?

[NISTECH]

this is a common problem with the evap as chris said, the key is when you test the vent valve it should close the first time you apply voltage to it, dont hit it twice with voltage as that may make it close. the system tests it self when you are driving down the road I believe about 17 mins after warm up or later. it does once per warm up cycle but certain conditions must be met before it will test[very specific conditions on your particular year] it will only apply the voltage to it once so if it does not seal it will fail the test. what we generally see if the pintle inside the tube becomes rusted and wont slide properly to seal the hole. That valve is only used to test the system otherwise it serves no purpose. it is always open unless it is conducting a self test for leaks.

[NISTECH]

something more too. did you buy a nissan gas cap or an after market one? I have seen several new after market gas caps not seal properly even when tightened.