Hello All:

I'm helping a friend with his 1982 Trans-Am installing a Knight Rider Dash.

Before all the testing and probing, the service engine soon light was coming on in run before starting the car. I even had it flashing a code 12.

Since all the work, the light will not go on. Following the diagnostic flow chart in a 87 factory shop manual, I tested the light circuit every which way.

My understanding is, that in a working SES circuit, the light will come on and stay on if the ECM is disconnected. The ECM grounds the light driver module, and a transistor turns the light off.

I tested the pink/black power and the black ground at the light driver module under the passenger side dash, and I tested the yellow wire. The light lights when I ground the yellow wire in the ALDL, and the light stays off with the ECM disconnected.

I conclude that I fried the LDM at some point while I was working on the car. Or, the cluster's printed circuit was so bad before I repaired it that maybe it shorted the wires and fried the LDM.

Does anyone have experience with this nightmare issue?

Thank You,

Lee B.

 

I'm told that it's true that if the SES light is messed up on 82 cars (and maybe other early years) that the ECM cannot properly communicate for engine repair and diagnosis.

I fixed the issue with a new light driver module, $30 from GM. The part number was a good number on the back of the old board, it's eight digits.

The new board is a slightly different design and you have to remove a black plastic pin from the blue socket the board goes into before the new board will fit.

You have to pull off the blue plastic part that keeps the black pin from being removed.

I hope this helps someone else...

Lee B.

 

Hi there I need a new light driver module , can you send me the part number ?

This post just helped me figure out what that blue box was. The module is missing on my car for some reason.

 

Send me a PM for details if you still need one.

 

Thanks for the offer John in RI, I appreciate it . I just noticed your response but I already obtained one. This post really helped me out with the issues I was having. My light driver module was completely missing from the car so I had no SES lightage at all and I also would get no communication with the ECM either. I replaced an ECM that was functional thinking it wasn't working but in reality it was just the missing LDM. Who woulda known.

 

No Problem,.... Glad it's all sorted out now !