So far I have had this code since late May of this year. I have had a smoke test done on the car, and changed the gas cap a couple of times. My problem is that the car would sometimes clear up the light itself, and it would stay off for a week or more. Afterwards, the light would re-appear, and stay on sometimes for two weeks or more. I was hoping that the smoke test would reveal something, but the mechanic said that the pressure was fine with no leaking, and to check the gas cap. He reset the light, and I changed the gas cap (I had a GM locking gas cap, and I went back to my original), and the light stayed off for 8 days until tonight.
Any clues to what the problem could be and how to solve it. I am getting fed up with chasing this problem, and I don't want to pour anymore money into it. My inspection is coming up in a month, and I won't pass it with this light on. Any input would be greatly appreciated.
A fairly common cause of errant P0440's is a faulty/failing fuel tank pressure sensor. If this sensor fails in a low vacuum state, becomes disconnected or otherwise opens the signal circuit the pcm will sense a gross leak...no matter how much vacuum is applied to tank the sensor never changes. and sets the P0440. If you have access to a scan tool access EGR/EVAP data and look at the fuel tank pressure sensor value. remove the gas cap, this value should noticeably change. if it doesnt or isnt near zero with the cap off you mostlikely have a FTP sensor or wiring issue. Also be sure to inspect for the following :A missing or faulty fuel cap
A disconnected, damaged, pinched, or blocked EVAP purge line
A disconnected or damaged EVAP vent hose
A disconnected, damaged, pinched, or blocked fuel tank vapor line
A disconnected or faulty EVAP canister purge valve
A disconnected or faulty EVAP vent solenoid
An open ignition feed circuit to the EVAP vent or purge solenoid
A damaged EVAP canister
A leaking fuel sender assembly O-ring
A leaking fuel tank or fuel filler neck
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Thanks. I will check those things out. Funny thing the light went off today. I am going to check the wires to the canister valve solenoid, and possibly replace it if it looks faulty. One of these days I'll get to the bottom of this annoying problem.
Another vote to check the wires. My wife's 01 LS threw this code and thanks to some suggestions from JBO members, I checked and sure enough the wires were broken loose from the evap purge valve solenoid.
good luck
