P0865: Transmission Control Module Communication Circuit Low
What to do
Expect a fixed gear and multiple warning lights. The breadth of the fault list is a clue to a single shorted wire, not evidence of widespread failure.
What this code means
The transmission module's communication circuit is held low, usually a short to ground. As with P0861, a bus line shorted low silences every module on it rather than one, so a scatter of communication faults across the vehicle is the expected picture and points at the wiring rather than at the modules reporting it.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Damaged data bus wiring · specialist
Less common
- Corroded transmission connector · moderate
- Faulty transmission control module · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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