PO440 code

[_J_]

My 2001 LeSabre has been displaying a loose gas cap warning on the dash, and a PO440 code. A dealer ran a vacuum test and everything is working ok with no leaks. The car also has a new Delco gas cap.

The dealer is stumped. Any ideas?

[Flatrater]

I have done several hundred of these problems and I have yet to have one stump me.

Now just because you have no leak under vaccum doesn't mean you can't have a leak under pressure.

Another thing that could show that you have a leak is a faulty fuel tank pressure sensor or you can call it a FTP sensor. This sensor is what determines if you have a leak. What the PCM does is close the vent valve and opens the purge valve starts pulling a vaccum, then the PCM closes the purge and looks to see a change in the FTP sensor, no change will store a P0440.

I have seen the fuel sender seal cause a leak and it is hard to pick up using the Evap test station.

The dealer needs to use the flowmeter on the test station to be sure your car has no leaks and that the FTP sensor changes with pressure and vaccum applied.

[_J_]

Thanks, Flatrater. I really appreciate your help.

The dealer said it holds a vacuum and they did a pressure test to 10psi. The service manager said a smoke test was also done. I thought he was pulling my leg.

I asked if there was a sensor in the tank and they said it was reading the correct pressure. They thought if it was the sensor, it was an intermittent problem. But, the gas cap message stays on all the time. Sometimes the check engine light comes on, but its usually just the gas cap message on the display center. There was one time that the message and engine light both went off while the engine was running, and was fine for a few days.

When the computer gets cleared, there are no problems for a few days, then it comes back.

I'm thinking of going to another shop, but hate to pay another diagnostic fee just to hear the same thing. I have some ideas now, thanks!