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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1513
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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I have a 2004 2500HD that first lost backup lights, then

Customer Question

Hello,
I have a 2004 2500HD that first lost backup lights, then daytime running lights, PRNDL indicator, tow haul function, and the trans temp gauge stopped working. I have researched it and believe it is due to my class2 serial wiring but can't seem to figure it out. The truck has a P0700 TCM trouble code
Submitted: 9 months ago.
Category: Chevy
Expert:  Juan Crespo replied 9 months ago.

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Yes, there seems to be a problem with the wiring between the TCM and the Allison (code P0700 is just a request to turn on the MIL). Other than plugging in a TechII to see what's going on with the specific signals, you could disconnect both ends of the harness and give them a thorough looking over, specially the one at the Allison. Make sure everything is clean and tight - no loose or bent pins, no corrosion or dirt. While you are at it, do the same with the PRNDL switch connector - back-ups and gear indicator depend on this one. Other than that, I strongly recommend plugging in a TechII before we start replacing any components.

Please let me know if that helps.

Best Regards.

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