Hey Guys,

I've been unable to resolve an inoperative Check Engine Light on my 85 Trans Am. Its an LG4 Carb 5.0 V8

I can only get it to come on if i ground pin D on the ALDL.

Here is what i know

• I've been troubleshooting and it has lead me down the path in yellow in the diagram.
• I'm not sure what test for "open" means, but when i grounded terminal "D" i got 12 volts - does that mean its not open? i.e i need to replace the Lamp Driver.

The car runs EXACTLY the same with the ECM plugged in or out, does that mean my ECM is also fried? Or is that because of the lamp driver?

So lost....

 

If there is continuity from D to ground the lamp driver module is faulty.

 

Any way to repair it? I'll try to find one online today.

Do you think my ECM is fried also? (Seeing as there is no difference between having it plugged in or out), or is that because of the lamp driver?

 

I don't have a schematic for the lamp driver, is the mc solonoid clicking KOEO ?

 

Hey,

Yes the MC solenoid clicks for about 20 seconds then off with KOEO, i "think" it does this also with the ECM disconnected. I can check later.

 

Can confirm - No clicking with ECM disconnected.

I think i may have found the culprit for the check engine light though.

Looks like a transistor on the Lamp Driver is blown, i never noticed it before.

Check it out... I've already ordered a whole Lamp Driver module from Amazon, but maybe i could have just gotten the transistor.

 

That's a easy circuit. Makes you wonder why it wasn't incorporated into the ECM.
You may have better luck identifying the transistor on the new LDM or can unsolder it and see if it's a npn or Pnp or just instal a 2n2222 and give it a try.

 

Update - this was a faulty lamp driver. ECM was perfect - passed smog today!