Original post by: Jeffery ,
Clean ALL electrical connections you can find (ie. bulkhead plugs, ground-to-frame, alternator leads, ECM plug). There is a code troubleshooting guide for DDEC engines ( http://www.dmbruss.com/images/Schematics/DDEC/0_Table_of_Contents.pdf ). Maybe you can find one for your engine. This is how me and Valley Power in San Diego solved my similar problem. Wiring issues can get REAL expensive in the labor charges. I was considering a new harness until we got lucky and found the problem in the bulkhead communications link plug between the ECM and the cab. Good luck to you.