The Car Care Clinic with the Dr John

98 Chevrolet - Check Engine Light Problems

Question

Dear Dr. John, I have a 1998 Chevrolet my check engine light keeps flashing on but not every day. Do you have any idea what would cause this, and what I have to do about it?

Answer

Hi Ray, Most times this first starts to happen on highway trips and 90% of the time this can be attributed to the O2 sensor ( Oxygen sensor ) but that's not to say it is always the main cause, most garages after they have performed a ' fault code review ' will get this code up with other codes and will change this first. The light may go out and come back on 2 days later. So there may be a miss-diagnosis here, and a waste of money for you. If this ever happens to you on future occasions always remember to ask for your parts back, they belong to you anyway. If there is a dispute over the problem remaining you have still retained the evidence that your 'old ' part most likely still works and wasn't the problem.

With the check light being on all the time there is no quick answer, more diagnosis needs to be done to determine the ' real ' cause. What this light does in coming on shows that input from one or more engine sensors is reading outside of its normal range, or that it has failed. This will trigger a malfunction circuit in the ECP ( engine control processor ).

The sensor may or may not be the primary cause. A failure or fault in other engine systems could create a condition that will cause a sensor to read out of range.

To really determine the cause of your problem. I would first have the check on the ECP for ' fault codes '. If there is none, I would suggest an analysis using a vehicle analyzer.

Good Luck!
Dr. John