OK. Last night I received my eprom from gmpartsdirect. I disconnected neg batt term. Installed chip, started vehicle and what do I get 10min later? That'* right a C/E light. Probally reading the QDM code 640 again. Now what? How bout an O2 sensor I am so confused now. :?

I think we're on the right track. This is a really frustrating one. I'd be wondering about the PCM itself, not just the chip at this point. Shotgunning that would be far more expensive than a full parameter scan. You need a professional to look at this before you spend any more money. The chip was a good first step, but that'* alot more cost effective than anything else it might be.

Get a FULL scan.

I just ordered a O2 frm GMpartsdirect.com out of frustration and bec I have 77,500 miles. Yes when the c/e light is on I feel a slight restraint at WOT but thats it. I had it scanned. The guy at the shop has 1 of those $2000.00 red scanners w diff cartridges, etc. I forget the brand name but he drove the car around with it hooked up and it told everything like the vehicle temp, rpms etc. What does the QDM do anyway?

What'* the website for granprix owners? Buddy here at work just bought one. Back to the topic: The mechanic was only able to say that the QDM was in the ECM. He was driving. When I told him I replaced the ECM he said maybe I replaced it with another bad one. But what'* the chances of replacing with a unit that has the same xact problem?

Ok. Let'* say for the sake of argument that yes I did buy another bad PCM with the same problem as the last. If I buy another from let'* say gmpartsdirect, is it a returnable part if this doesn't fix my problem? :( :?