Questions and Answers

Grand Am Check Engine Light Q. Dear Vince, I have a 1989 Pontiac Grand Am 2.5 liter, 5 speed with about 140,000. VIN 1G2NE14U5KC672197. The car was operating just fine until the return trip from dropping the kids off at school. The car speedometer failed and the check engine light stays on. I noticed the fan on the radiator was on even when the car engine was cold to the touch.

I recently installed new TPI, AIR VANE, AIR INTAKE TEMP sensors. I will add the car got excellent gas mileage last week and now smells rich. I suspect this is a relay or speed sensor problem. Would you please advise with some detail as I am just a junker mechanic.

Thanks

A. With the speedometer dropping to zero and the check engine light coming on, I think it's a pretty safe bet the Vehicle Speed Sensor (VSS) died on you. Since the computer uses vehicle speed as part of the fuel management program, it can not regulate the fuel, thus your higher fuel consumption.

You can get the DTCs the computer has stored by grounding the diagnostic terminal (ALDL terminal A to B). The "CHECK ENGINE" light should flash a Code 12. This is displayed, on the check engine light, by 1 flash followed by a short pause then 2 flashes. This should repeat 3 times. A Code 12 should always flash when an on-board diagnostic check is performed. Any other codes, stored in the computer (ECM), will follow a Code 12. A bad VSS will display a DTC 24.

To clear the trouble codes from the memory of the ECM, either to determine if the malfunction will occur again or because a repair has been completed, the ECM power feed must be disconnected for at least thirty (30) seconds. Depending on how the vehicle is equipped, the ECM power feed can be disconnected at the positive battery terminal "pigtail," the in-line fuse holder that originates at the positive connection at the battery, or the ECM fuse in the fuse block. The negative battery terminal may be disconnected, but other on-board memory data, such as pre-set radio tuning, will also be lost.

Additional Information provided courtesy of ALLDATA