Sorry to open up an thread, but I'm getting the same issue on the same car. P0440 on my 02 Cavalier.

We already replaced the gas cap as a easy first attempt. Code still came back.

I unplugged the line at the TB and we used an air tank to blow pressure into the lines. All we found was a hissing noise at the top of the fuel tank. I haven't dropped the tank yet to see what'* going on up there. But I'm assuming there'* some sort of pressure relief up there, right? Since we were pushing 20-30 PSI into the system, I'm figuring that was a bit too much.

Where is the fuel tank pressure sensor? Is that the smaller of the two boxes behind the tank? Or is it on top of the tank?

Any help here would be much appreciated...after spending each of my last two weekends working on the car for various other reasons, I am at my wits end with this problem.


Secondary question: how long does it take for the computer to read the error? I've had the light come on in between 35 and 45 miles after reseting the system. What is the minimum mileage to get the computer reading the system? The reason I ask is due to the fact I need a NY State inspection and I can't get by the sticker computer with the CE light on...

Thanks in advance!

Moderator, please move this to a new thread.

When you replaced the gas cap, did you purchase an after market one, or get an OEM from the dealer?

Both, actually.

My dad grabbed a cap from AutoZone and we tried that.

When the code came back, I got an OEM from the dealer.

The code still came back.

Honestly, though, I was just hoping for the best there. The O-ring on the old cap looks like it'* in pretty good shape and the spring valve was tight and moving freely. I'm rather positive it'* not the cap causing the problem...unless I have 3 bad gas caps.

Sorry if I am pointing out stuff you already tried, but I like to check the easy stuff first. Check the sealing surface on the top of the fuel tank opening where the gas cap seals. Try cleaning it up and applying grease to ensure a good seal to the gasket on the gas cap.

No problem. Yes, we've tried that as well. I'm 98% sure that the cap is not the problem here.

Read this thread:

https://www.gmforum.com/obd-ii-trouble-shooting-153/p0440-284087/

Posts moved to own thread.

actually in ny you can have 1 not ready indication, so if you have a scanner clear the codes then drive it around until all the other ones go ready, evap is the last system checked, ive snuck my bonnie through the last few years that way.

I've toyed with that idea the couple days. But how would I know when the other systems are ready? That'* the trick.

my scanner has a "readiness indicator" you just wait till all the systems show ready