I have a 99 Pontiac grand am. The service engine light stats on but shows no code. What's wrong??

Asked by May 25, 2013 at 08:30 AM about the 1999 Pontiac Grand Am 4 Dr SE Sedan

Question type: Maintenance & Repair

There car runs quiet and smooth the rally lights
don't work other than that nothing seems wrong.

4 Answers

77,855

If the service light is on then there must be a code unless the computer or wiring is messed up.

56,595

Have the computer scanned. Auto parts stores like Advance and Autozone will do it for free. Post the code(s) here and we'll be able to help. Could just be a faulty sensor. Since the car is still running good it's probably nothing serious. HTH. -Jim

155

I have the same issue, but for me it turns on and then after a couple days it turns off. these Grand Am cars are very faulty I think im just going to get a different one soon

56,595

If there is no code, the circuit that feeds the bulb must be shorted to ground. A light bulb has two terminals. One positive (+) and one negative (-) also called ground. The positive side of the bulb for the service engine light is on whenever the ignition switch is turned on but is not grounded to complete the circuit to light the bulb. The bulb is grounded by the computer when the ignition switch is on but the engine is not running or when a fault is detected. When a fault is detected the light comes on and a code is set and stored in the computer. Since there are no codes either the ground wire that feeds the bulb is worn and touching something metal, the printed circuit behind the instrument cluster is bad, or the computer itself is malfunctioning. These are the only things, to my knowledge, that will illuminate the light but produce no trouble codes. HTH. -Jim

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