Truck failed CA smog! They said it failed the EVAP test? What would cause my truck to fail the evap test? What should I check out?

Thanks

 

loose gas cap, just get a new one

 

thanks for the reply. But they test the gas cap, and the gas tank separately... the cap passed, the tank and whatever else goes with it test didn't. Any other ideas?

 

The EVAP system consists of the following:
Pressure Relieft/Rollover Valve (tank mounted) This is used to relieve fuel tank pressure as well as prevent the flow of fuel through the vent lines in the even of a rollover

Evap Canister (front of engine compartment, passenger side). This is used to temporarily hold fuel vapors until drawn in by the engine.

Evap Canister Purge Solenoid (located on the firewall on I4's, located to the left [drivers side] of the throttle body on V6/V8) This is what is used to "empty" the Evap Canister. The PCM regulates this by providing a ground for it. When the PCM gives it a ground, the solenoid prevents engine vaccum from reaching the canister. Likewise, when the PCM takes away the ground, the solenoid allows the engine to take in from the canister.

During the warm-up period, the PCM will provide a ground so that the engine does not take in from the canister. After the engine reaches appx. 80*F and a time delay of appx 100 seconds, the PCM will remove the ground.
Under certain conditions, the PCM will apply or remove the ground to the solenoid.

Probably the solenoid. Or maybe the canister. Try pulling codes to see if it comes up with anything.