Quick EVAP question

[Sunfire 02]

Hello just a quick question my girl owns an 02 sunfire and her engine light came on and i checked the CEL it stated P0442 - Evaporative Emission (EVAP) System Small Leak so i figured that she simply needed a new gas cap so i cleared it put the new cap on and now it has reappeared any idea where i should go from here?

Thanks

[Blue Bowtie]

Test the tank pressure/vacuum at the test fitting in the engine compartment (the fitting with the green valve cap). After warm up, the vacuum should be about 0.1-0.4" Hg.

[Sunfire 02]

from what i understand it could only be a couple of other things that could be leaking such as the gasket around the fuel pump housing or the goose neck that comes up to the gas cap needs replacing. Is there a test that a shop could run to find out what it is befor i start throwing parts at it? And if so how much should i expect to pay????

Thanks

[Blue Bowtie]

A shop will start the diagnosis similar to the way I described. They may actually read the tank pressure/vacuum sensor via a scanner, but should verify the tank sensor reading with a mechanical vacuum gauge to be sure (the tank may have vacuum as it is supposed to, but the sensor may not be reporting it). The test results would determine the next step in the diagnosis.

from what i understand it could only be a couple of other things that could be leaking such as the gasket around the fuel pump housing or the goose neck that comes up to the gas cap needs replacing.

There are other potential causes In addition to those possibilities. The tank vent solenoid valve may also be stuck open. The tank pressure sensor 'O' ring could be leaking. An evap canister hose or vapor/vent hose could be damaged or loose. The evap canister itself could be cracked or damaged. Or the tank itself could be damaged. There is also a possibility that the vent solenoid valve is being held open by the PCM, but that would be a remote and rare possibility.