Chevrolet Repair Questions? Ask a Chevy Mechanic for Answers ASAP
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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.