My o5 duramax just started putting out three codes. I am looking for help with where to start looking. Codes are P0700 Trans control sys malfunction, U0073 Control module comm. bus off, U0100 Lost comm. with ECM/PCM module A. Any help would be appreciated....Thanks

 

You need to check the buss bar fuse under the fuse panel under the right front side of your hood. It is a 100 Amp fuse that you must take the curved brace off to check. Release the main fuse box clips and you should see it. When that fuse blows the transmission cannot communicate to the ECM. Hope this helps you.

 

Hopefully he's already fixed it within the last year.