Hello,
I just bought a 2004 GMC Sierra Duramax. I bought it to tow our family trailer on road trips. After a short test trip, The one thing I noticed was that the temp gauge was really erratic and would peg to overheating and the overheating warning would come on but engine was clearly NOT overheating and ran fine. I suspected a problem in the instrument cluster. I took it to the shop to have this looked at and also for a general check-up. They fixed several things on the engine, oil cooler& pan leak, new water pump, as well as replace most of the steering components. Next they said the computer (ECM) was bad and when they sent it in to be rebuilt, the company said it was to destroyed to be rebuilt. I decided to bail out there, I now have the dead truck and old ECM in my driveway. I want to be sure there is not another problem (electrical?) that is causing the ECM to fail, before I drop more cash for a new ECM just to have it burn up. From what I understand (I may be wrong) ECMs don't commonly fail on their own. I have spent almost all my extra money in this so I need to get this fixed myself. I am a decent mechanic, but don't know where to start on this. Are there common electrical issues I can check before replacing the ECM? Could the instrument cluster be a problem? Did I mention this is my first GM and first diesel? Trial by fire I guess. Any advice/help would be greatly appreciated.
Thanks, Matt

 

I should add the previous owner took the exhaust off at the downpipe, and jerry-rigged a straight pipe from there. Not sure if that could effect the ECM. I will be replacing that mess as well

 

The ecm is 15+ years old. I'd not think it would be to exspensive to replace.