Questions and Answers

Celebrity SES Light Q. I have a 1987 Chevrolet Celebrity 2.5 liter 4-Cylinder car with about 103,000 miles. It seems to run fine. However the Service Engine Soon light comes on occasion. Sometimes times it blinks and goes away. Others it is there for the duration of the trip. Any ideas on what is causing this?

A. There are many things that can cause the Service Engine Soon (SES) light to come on. What has happened is that the computer has detected a malfunction and is using the SES light to alert you to the problem.

When a fault is detected, the computer stores a trouble code. This DTC can be retrieved and will tell you what is causing the light to come on.

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.

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