I've heard that if the CES light does not come on once the ignition is on the on position, it can be either a burnt out bulb, or a bad ECM.

Where would you put your money - a bad ecm after 16 years and 175000 miles, or just a burnt bulb.

I know the burnt bulb SHOULD be easy to check - but I can't remove it without at least 2 hours of work in this peticular gm application. Also, if it's any consideration, I've been losing speedometer function every now and then as well (and when that occurs, the TC unlocks.)

 

Dead bulb is more likely. I take it the vehicle has a digital speedo? If so then its probably a fault with the VSS or some other part of the circuit since the ecm looses the pulses as well.

 

I thought the same thing, but it just doesn't add up that if I bash the top of the dash, that the speedo will all of a sudden come to life and it be a VSS failure.

Maybe if someone else has had asimilar experience, and it was indeed the VSS, I will definately go that route, but I would like to know before blowing $30....

 

Is teh speedo mechanically driven or digital?

 

Electronic - VSS at the tailshaft extension.

 

i can't recall on my '91 with electronic dash stuff, but the light is probably one of those "integrated" types that come with a socket that need to be replaced from the rear of the dash panel. not too hard, just a little time consuming, but would definitely go there first to check the bulb. just my .02.

KAM

 

See if a scan tool will connect to the ECM. If so then the ECM is most likely good.

RBob.