I've been reading a few posts and everyone says when checking for trouble codes to stick the paper clip in but don't start the car. And the starting the car was stressed. Is it really bad to do that?

 

Arawn,

It is possible to damage the ECM by attempting to start the engine with a jumper in the ALDL diagnostic terminal. GM stresses this in their service procedures. I haven't dissected the circuits to see exactly why, but I'll take their word for it.

I'm guesing that the reduced system voltage from cranking may have something to do with it, or the fact that grounding the diagnostic terminal while running is a request for Field Service Mode, not scan. The ECM dumping error codes while the engine is cranking may cause problems with the firmware, but as I stated these are all just guesses. I know some members have done so inadvertently and not damaged the ECM, but I wouldn't risk it.