Evaporative Emission System Question

Jul 17, 2006 8 Replies

Check engine light came on the other day, code P0442 -- slight evaporative control system leak. 2001 Jetta GLS with 2.0L engine.



My question for you experts is -- is there a particular part or condition that typically causes this? In other words, is this one of those well-known things, like coolant-temp sensors, that you can zero in on right away?



Your expert advice is, as always, appreciated.


AFAIK gas cap maybe? ;-)

or you might need a vag-com tool (ross-tech.com) to help diagnose what's wrong. It might be a bunch of different components that could cause that DTC. hoses, charcoal cannister, pump or valve or ???

Bentley repair manual can help too.

good luck,

yeah the gas cap is the easiest thing but replacing that is pure guesswork really. Might not be it and that'd be ~$30 or so down the drain if it's not it.

that code basically means the system detected a leak at or near your fuel tank. Doesn't mean fuel (liquid) is leaking out but rather than there are vapors leaking out because it depresurrizes on its own. could be gas cap, could be something else.

Of course if the gas cap has not been put on tight, that would be a good thing to change and see what happens. Turn it until it clicks, and NEVER top off the tank.

Yep. Might take a few driving cycles at various speeds to reset the light though if it was the cause (don't necessarily expect it to go away immediately).

Not the gas cap. Apparently, this is not one of those common things, with a well-known cause. Thanks!

OK how do you know that it is not your gas cap? Did you make sure that it was not damaged, tight and clear the faults?

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Well it is time to test/check the Evap system. Need to make sure that all the valves/pump/hoses are functioning and leakfree. It helps if you have a tool so you can do an Output test and test components.

Have fun and let us know what you find! later, dave (One out of many daves)

Yes, checked it out, re-set codes. Plus, due to my driving off at the pump one day with the old cap hanging on the filler door, the cap is relatively new (doh!) -- it is an OEM cap, bought at the dealer.

It sho nuff is. I'll start with the ol' sniff test.

Well I guess that rules out the cap. lol

I usually apply some very low pressure air to the hoses and listen for leaks. That cannister is usually a little hard to get to on some VWs. Did you do the Output test yet?

good luck and let us know what you find.

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