How long should your service engine light be on?

I noticed on my 95 Aurora that the "Service Engine Soon" light comes on just for a second while I'm starting the car. On my Delta 88 you turn the key on, not cranking it and the light stays on for about 3 seconds.

How long should these lights be one and should it come on before cranking the engine. It has not come on at all since I have owned the car.

Thanks,
Bobg

I wouldn't worry about lights staying on for 3 seconds. Not much of a difference form one second. If it stays on, then there is a problem.

It should not be on at all.

The check engine light should come on when you put the key in the run position before the start position. All system lights (idiot lites) should come on for brief period a this point. A lot of people just don't notice since the put key in and turn to start position then release. Some cars, not all, will stay on after the key springs back to the run. I believe that this is the case with all GM's. The owner's manual should address this issue.