p0440 - Odd solution

[hufhouse]

A few weeks ago, I posted that I was having code P0440 Evap Leak.

I replaced the gas cap. Code came back.

I replaced the vent solenoid. Code came back.

I took the car to an independent mechanic without the best selection of computerized tooling. He tested the solenoids using a 9v battery, and they were working. He visually checked all the wires and lines, and couldn't find a problem, so he didn't charge me and told me to go to someone with a better computer and smoke tester.

I took the car to a better-equipped mechanic today, and they put it on their computer and couldn't command the (new) vent solenoid. There was no current at the solenoid. They checked the wires all the way back to the fuse panel, and they were good. They checked the fuse, and it was good. They put the fuse back in, ran the test again, and everything was fine.

As best they can figure, the fuse was not making contact and leaving an open.

Strange.

Oh well, it only cost me about $60 for the diagnosis.

[hufhouse]

Well, so much for the problem being resolved.

Evidently, unplugging the fuse and plugging it back in must have "rebooted" something, because the SES light is back on.

The vent solenoid is working, but it is not receiving the command to close from the ECM during EVAP testing.

Am I going to have to get a new "computer"? Could this just be some kind of ground problem? Any suggestions?

[hufhouse]

I wanted to bump this back up and see if anyone has any info to share.

If I unplug the fuse for the vent solenoid and plug it back in, I can go for a few days without the SES light. However, the vent solenoid eventually doesn't respond to the command to close and the SES light reappears with code P0440.

The vent solenoid is good. (In fact, it's new.) As I said in the previous post, if we remove and replace the fuse, the mechanic can command the vent solenoid. Then, it stops working again.

Computer?

Fuse panel?

Short?

Open?