My check engine light came on. Car running fine. Checked for codes. Only flashes code 12. Original GM service manuel suggests a short to the ground in the light control CKT 419. I am not a mechanic, nor an electrician. Unsure how to verify a short, and/or how to fix it. Is there anyone able to point me in the right direction?

 

What year? I am assuming a pre 95? Number 12 on an obd1 is key on, not running.

 

Yes, 1989 cavalier Z-24. 2.8 liter V-6. I have the diagnostic tool, code 12 flashes to indicate the system is working before it flashes trouble codes. key on not running. It was recently suggested to me that while the ECM may be functioning properly, the computer prom may not be. I pulled the ECM and the prom is a Hypertech chip I purchased in the early 90s. So its possible this could be my problem

 

My CEL has been on for many years - I could care less. The car runs fine, I keep the oil and fluids clean - end of story.