I just got an 04 GMC 6.6 and don't really know much about it except that it had two codes come up with no check engine light. The first code is p-0380 glow plug feed back circuit. did some research and found it could be anything from the module to a bad glow plug. Is this a serious problem to run the truck. The other Code was p-1621 have no idea what this is except a control module long memory performance code came up? again don't know what that is! If yall could help me out with any info on this truck I would greatly appreciate it. I don't even know what rear end it has in it.

 

those codes aint serious probs. Im guessing truck is lb7? (8th digit of vin will be a 1) usually glow plug circuit probs set a check engine light. Those codes may be history codes. Id clear them out and see if they come back. the rear end should be a AAM 11.5

 

thanks for the help!

 

you can look up the RPO codes on the tag in the glovebox, that will give you gear ratio and other options the truck has, code G80 is the "locker" thats only a locker till 20mph

 

i don't know if you figured out your glow plug problem yet but i have been running mine with the glow plugs unplugged and the code turned off for about two years now with no problems. starts up right away even with the temperature down to 14 degrees. live here in sunny taxifornia so cold start is not really a problem for me anyway

Jason