P0440 uhg - 2003 Chevy cavalier

I have a 2003 Chevy cavalier. I’ve been having an evap system code. Got it to shut off for like a week then it came back. Replaced : gas cap, purge valve, vent valve, inspected hoses, leak check(vapor). Have not replaced gas pump seal (don’t smell gas), have not replaced canister, I’m going to inspect the wires on the undercarriage this weekend, then I guess my next replacement gonna be a map. I really don’t want to replace canister if I don’t have to. Not cheap. But damn this is annoying. Thoughts? ( this was my girls car she never took care of it )

If gas got into the canister at any point, it will have to be replaced… it’s designed for vapors only, not liquid… that’s the extent that I can help you. Good luck!

A defective fuel tank pressure sensor can cause that code.



The way it works, when it decides to do a test to see if the evap emissions system is properly sealed, the computer commands the purge valve to open but leaves the vent valve closed. The engine vacuum then causes a vacuum to form in the evap system. After a while the evap system has the proper vacuum level, then the computer closes the purge valve and waits to see if the vacuum holds or not. If it doesn’t it sets that code, which is for a large leak. It does this test before the engine is fully warmed up, and only when the coolant temp and ambient air temp are within 9 degrees of each other. The vehicle speed must be less than 75 mph, and the fuel tank level must not be at either extreme. The code will be turned off if it passes the test 3 times in a row. The way the dealership figures it out is they use a smoke machine to inject smoke into the system, then they open and close the various valves and look here and there to see if there’s any smoke escaping. Similar to how you’d quickly find where the leak was in a basketball by holding it underwater and looking for bubbles.

I presume you have neither a smoke machine nor a pro-level scan tool that allows you to open and close the valves on command. In that case about the best you can do is inspect the rubber hoses for cracking, failing connectors, the service-port schrader valve, and to make sure the vent and purge selenoids open and close when their control voltage commands them to.

It’s a 2 hour job to replace the pressure sensor, tank must be removed, but you might be able to do some measurements on its signals. Verify it is getting the a 5 volt reference, and it outputs an output signal in the range of 0.1 volts to 4.9 volts, the output voltage is inversely proportion to fuel tank pressure.

I’d suggest to focus on looking for leaky and/or kinked evap hoses first. If nothing found, hire out the smoke machine test.

Most of the lines in the front of the car are molded plastic. Which I’ve never really likes for vacuum lines. No, borrowing store code reader till I. An afford to replace my old code reader. I did a brief visual inspection of lines and well as sprayed a bit of starting fluid in the general area while running and no change in idle. I have yet to crawl under car this weekend. Which I will do with my dvom as well. I’ll let y’all know what I find. Ty for the help