I got a check engine light for a small evap leak (p0442). Cleared the code and it comes on about two days later. I replaced the fuel cap and looked at the evap house coming off the intake to some sort of valve and then to the charcoal canister. Light still comes on. I don't see anything wrong. Does anyone have anymore ideas? Car is a 2004 Scion Xa manual trans.

 

These are the areas to check for 0442:

Vacuum hose has cracks, holes, or is blocked, damaged or disconnected
Fuel tank cap incorrectly installed
Fuel tank cap has cracks or is damaged
Open or short in vapor pressure sensor circuit
Vapor pressure sensor
Open or short in VSV circuit for EVAP
VSV for EVAP
Open or short in VSV circuit for CCV
VSV for CCV
Fuel tank has cracks, holes, or is damaged
Charcoal canister has cracks, holes, or is damaged
Fuel tank over fill check valve cracks, or is damaged
ECM

Cheapest fix is check vacuum hoses for cracks and proper placement.
Replace fuel cap or fuel cap gasket.
test the two vacuum switching valves - one you see in the engine bay, the other is on the charcoal canister. If one, the other, or both don't click when battery voltage is applied, they're stuck open or closed and probably need to be replaced.

If the canister is cracked in some way it will have to be replaced.

I've had a vacuum switching valve go bad on a camry and replacement fixed the recurring code.

According to xB repair manual the 0442 code is for a detected leak of .04 inch or larger. So it's not much.

The two valves control the direction of fuel vapors: to the charcoal canister from the gas tank when the car is off, and from the gas tank and the charcoal canister to the intake manifold when the car is running.

Good Luck,

MD

 

The small evap leak is a pain to find. If you can find a garage who will let you borrow their fogger, that will help quite a bit.

 

Great info: cherry-8! Will keep this for future.