I want to reset the service engine light on my 2000 Pontiac Bonneville. I get a 'check gas cap'notice on the the dash. I replaced the gas cap with a new 'dealer gas cap, but the service engine light stays on, and the check gas cap notice continues to stay on. I have gotten three suggestions to correct the problem.#1 disconnect the positive terminal on the battery for 30 minutes and the computer will reset. #2Ask my mechanic to reset it. #3 Drive for about 100 miles and it will reset itself. Help
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I am not sure how the heck the car knows if the gas cap is on or not. If there is a pressure sensor, it might be possible that the gas filler neck is rusted through at some point. Or, if there is a small hose leading back to the fuel door next to the filler neck, it might be rusted through.

Just speculations here. I know it is unusual for our Bonnevilles to have any rust.

It's a fairly common problem, generally caused by corrosion at the top of the filler tube where the gas cap seats. The easiest solution is to sand down where the corrosion is, and then put a little silicone lube in the same spot. This is a temporary fix, as eventually the warning will come back. Adding lube again will take care of it for a while. The other solution is to replace that part of the filler tube.

Disconnecting the battery will not reset the warning. Driving for a while may eventually help, as it will reset after so many passed tests. You could head to Advance Auto, or AutoZone to have them pull the code, and reset it. Buying an inexpensive code reader will allow you to do it yourself.

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*Gone, but not forgotten* - Black 2000 SSEi, HIR Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, 180 degree thermostat, HS 1.9 rockers, LSx yellow springs, Intense FWI, PCM, shift kit, push rods, and 3.4 Pulley. ZZP Power Log.

I had to troubleshoot some codes related to emissions on my 03 leSabre. The computer runs a leak test under certain conditions.


These may not be exact--it's been a while since I read them in the FSM.
The fuel level needs to be between 75% and 25%
The engine temperature is lukewarm. I don't remember the temp but let's say it's between 105 and 175 deg. In other words a restart after the engine was partly warmed up, I stopped for coffee on the way to work at a coffee shop, and came back out to restart. The emissions check ran and if it passed the leak test, the light was off. A dead cold start didn't run the check. A hot restart didn't run the check for air leak.

There likely are lots of other requirements in terms of other codes that can't be store, but those didn't matter.

Ive been told this is a common problem on Bonnevilles and LeSabres. Both mine (Bonneville) and my girlfriend's (LeSabre) cars do it. I notice it more when the vehicle is low on fuel. I had a Toyota that would kick the light on when it had 1/4 tank and it was below 40 degrees out.
The vehicle thinks the gas cap is off because on start up it "evacuates" the tank and tries to create a vacuum to collect fumes. If it can't create vacuum because of a bad gas cap or leak in the filler neck, the light comes on. I think under certain circumstances (cold temps and low fuel level) it takes longer to create the vacuum in the tank and the computer times out.