Service engine soon

Cadalic 1992 Devile

Light comes on I take to service people. Light is not on. Can’t get info if light is not on. I wait till light is on, go to service people, they have to turn car off to hook up equipment to test system. Light will not come on.

Light comes om 2 or 3 times a month. Car runs OK

How do I get it checked if light will not come on ???

If you go past the recommended oil change interval on some cars, the service engine light will come on, then go off again. The car will run OK of course. So I would check that part first.

Your computer should store the trouble codes that prompt the check engine light to come on (assuming this isn’t just a “maintinence required”-type light). Luckilly, you’ve got an OBD-1 car, so you don’t even need anyone to read the codes for you. Unbend yourself a metal paperclip and read on:

If you can’t get stored codes, you may need a new engine computer.

Not true whatsoever. Maintenance required lights will, but the service engine light comes on when there is an actual problem. They can go back off if the pcm runs a self test and the problem isn’t present at that time, but the oil change interval does not affect it.

Those lights are almost always related to an emissions component and probably have no effect on how your car runs or if you are doing any damage. But, you should probably get those fixed before your next inspection. But, if you had your car inspected and it passed, then it’s probably a faulty light or sensor.

It’s frustrating when you have a problem like this and can’t get it to duplicate itself for the mechanic. Only other thing I can think of is to wait until it gets worse.

In my scanner there is a selection called “History codes” I was brought a 93 Regal a couple of weeks ago which would downshift from 4th to third at various times at highway speed along with a service engine soon light turning on and off. Owner thought the trans was history and was ready to pay me for a rebuild. I scanned it when the light was off and got “No codes present” When I checked the history codes I got a code 21 Throttle position sensor circuit high. Scoped the sensor and saw it maxing out at 4.94v while idling in the driveway. $54 sensor and away he went.


I had an early 1980s Oldmobile company car which had an earlier version of this system and the service engine light would come on for oil change, as well as a “low coolant” light if the level dropped. It did not have a diagnostic system like today’s cars.