QuestionQUESTION: I have a 1999 Cadillac DeVille. From time to time the "Check gas cap" light and the "
Service Engine Soon" light come on simultaneously, stay on for several weeks and then go off. Some days later the cycle starts all over again. One mechanic said he thought I had a vacuum leak in the gas cap, so I had it replaced, but that didn't solve the problem. I think it sounds like an electrical problem. What's your best guess? Thanks.
ANSWER: Did you retrieve any CODES from the computer ?.
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QUESTION: No, I haven't seen any codes, and I don't know what the mechanic may have seen.
ANSWER: perform this test:
1. turn ignition key to the ON position. DO NOT start the car.
2. On your climate control panel you will see an OFF and a WARMER (^) button. Simultaneously push and hold these 2 buttons in for 3 seconds and release them.
3. You will see LETTERS and NUMBERS appaer and the they will finally stop.
4. Write down EXACTLY what you see on the fuel data display and let me know what you have.
5. Turn ignition key OFF.
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QUESTION: The first thing that appears is "PCM PO440 Current." Then a series of other items flash on and all of them say "no codes." Then the last thing that appears and stays on is "PCM ?" Does that help?
AnswerYou have a problem with your evaporative emissions system.
Fault could be:
Loose vacuum lines/hoses at the canister purge vent valve.
Fuel tank evap valve.
Evap control solenoid.
PCM computer.
You will need a diagnostic scanner and a EVAP PRESSURE/PURGE Diagnostic station which is a special piece of test equipment to test the system.
