98 Z71 serice engine soon light came on then went off?????

My service engine soon light came on this morning right when i cranked my truck up at 5am. It stayed on until i got to work and parked my truck, Then at 6pm i cranked my truck again to come back home and it was off. Any one know what happened?

also, i baby my truck . i never floor it but this morning i had to floor it to get around a semi , and i looked in my mirror and it blew some black smoke out so i let off and it quit. Then i did it again and it blew less smoke out. then the third time it didn't blow any smoke out and it hasn't since, Any one know what happened here?

Blowing the carbon out of the exhaust. That is good for an engine.

It's the new way to 'baby" your truck; didn't you know?!!

There are many things that can set the service engine soon light (a loose gas cap can set it!). If the PCM sees that the problem has gone away it will turn out the light. Since you have a 98, it is an OBD-II system which should have the code stored even though the light has cleared. Any Autozone will read the code for free.

//2000CAYukon

Yukon is correct, type A and B DTC'c will be stored in memory even when a passed drive cycle turns MIL light off. It may also return to on if two consecutive drive cycles fail. Example: My 98 K1500 would set a misfire DTC if I idled too long, but would go off if I completed two drive cycles without having to idle more than a two minutes. This would re accurr over and over until problem fixed.My fix was to trade it in and get a 2005.

Cadilakin, i hope your not back to leaving smart a$$ comments? i wouldn't wana have to get the webmaster back in here.

I don't think Cadilakin was being too smartish.
The Cadillac forum has a lot of comments from a powertrain engineer for the Northstar engine about WOT, which is wide open throttle to clear the carbon from the engine from the slow driving. It is highly recommended. At least for the Northstar.

Bob B

I don't think Cadilakin was being too smartish.
The Cadillac forum has a lot of comments from a powertrain engineer for the Northstar engine about WOT, which is wide open throttle to clear the carbon from the engine from the slow driving. It is highly recommended. At least for the Northstar.

Bob B


yeah it never hurts to get on it(the gas pedal) every once in a while.

The check engine light on my 97 will come on when it is really cold outside and stay on for a few days and then go off. The guy at autozone says it is something to do with my egr valve but I haven't noticed any difference in performance so I haven't had it messed with yet.

Originally Posted by sherman69
I don't think Cadilakin was being too smartish.

I know , i was just messin with cadilakin because of something that happened a while back.

I've been waiting for someone to give me a hard time!! Finally I get some love on here!!!!