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That Mystery Check Engine Light- Lamp Driver Repair Information For CCC Cars 2023-08-15

This discussion came up on another forum, and some good information came from it. Figured I'd share some findings here on this mystery lamp driver. If you have a CCC G-body car, you have this. From what I understand, it takes a 5V signal from the ECM and also boosts it to 12V to light the CEL when warranted. Basically, if the ECM loses its ground with the key on, the light comes on.

If you've ever had to troubleshoot a check engine light that is fubar, it may not be your ECM. It may just be that pesky little lamp driver for it. When you turn the key on, one of the immediate checks the car does is illuminate that check engine light (CEL) because when the car is on but not running, the ECM isn't grounding, so...CEL. Sometimes, that doesn't happen, and while the ECM may still operate the car, the lamp won't light up when you need it. The lamp driver also monitors the ECM and if it craps the bed, the lamp driver senses this and turns on the CEL. Prodedures in the chassis service manual has charts [Charts A5 (CEL lamp doesn't light) and A6 (CEL lamp stays lit) for B, G, and E body Oldses] which guides you to the issue.
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