98 Blazer SES Light On, P0440 Evap System Malfunction

[Allbert]

I've searched previous threads for some help on this one, but I haven't found anything that fits my problem for sure. I've got a 98 with 153000 miles on it, and lately the SES light has started coming on right at startup sometimes. The trouble code stored is P0440, Evap System Malfunction. First thing I did was buy a new gas cap and clear the codes, but it came back. I've cleared the code several times, and it usually doesn't come back while driving, but it will come on right at startup after sitting for a while, which makes me think it may be an electrical issue (like intermittent open circuit at a sensor or solenoid maybe?). I've removed and checked the purge solenoid on the manifold: good resistance, good connection, clicks with batt voltage applied. Same for vent solenoid at canister. I don't know where the pressure sensor is and my Haynes manual doesn't say, but I'd like to check it out too. Can anyone tell me where it is and how to check it?

[BlazerLT]

I would check for possibly a broken wire going to the wire harness.

Also, maybe the canister is shot?

[Allbert]

I was wondering if that might be the problem, but didn't know exactly how canisters would fail. I guess they do though or they wouldn't bother selling them as repair parts. Which harness do you mean... the one going to the solenoid at the canister?

[BlazerLT]

I was talking about the wire harness going to the solenoids.

Make sure they are not burnt or rubbed through somewhere.

[ricksza]

The pressure sensor is in the fuel tank module. It looks like a MAP sensor.

[Allbert]

Thanks to both of you.