Swapped in a 350 into my T/A, deleted ECM, etc. etc. Everything's all good except that the check engine light is always on now. I thought the ECM controlled it, so now I'm wondering why it's on.

Anyone have an idea why?

 

Did you remove the ECM from the car?

Easiest solution is to remove the Service Engine Soon ligh bulb.

 

That's what I did. Just remove the bulb

 

Yeah the ECM is out. Remove the bulb it is! For curiousity's sake, any idea what is actually making the light stay on? I thought the ECM controlled it.

 

I may be mistaken , and if so maybe a mod can delete this , but , I thought on the early third gens there was a "CEL driver module" separate from the ECM that took the ECM's signal and used it to control the bulb .

Course , at my age there MAY be the possibility I'm thinking of another car , but it sure sounds familiar to me from somewhere .....

 

Your not mistaken,

All Carburated cars had a "lamp driver" & the ECM signal was relayed thru the Lamp driver before reaching the bulb. This thing was usually taped way up inside the dash harness and not easy to access (at all !!). All FI cars had a direct switched ground wire from teh ECM to the C/E light.





When I converted my step-fathers MPF Firebird to factory LG4 carb I used the carb ECM harness and the MPFI dash harness. In order to get proper operation to the C/E light from the ECM I had to install a Lamp Dirver "in-line" off the C207 ECM wire.

 

This is correct:

The ECM doesn't turn the light "on"; it actually commands the driver to turn it OFF. Without the ECM, the driver module receives no such command, and keeps it turned on.

Just pull the bulb.

 

Thank You John and Sofa for confirming that my memory is correct on the CEL driver . Good also to know that it was carb. only , and yes , the one time I encountered this it was on a carb. 85 TA with a 305 ....

 

You are correct