P0864: Transmission Control Module Communication Circuit Range/Performance
What to do
Expect intermittent poor shifting and occasional warning lights that clear themselves. Ask for the module grounds and connectors to be checked before the module itself is suspected — corrosion distorts messages without breaking anything.
What this code means
The transmission module is communicating, but the messages are not what they should be — corrupted, incomplete, or arriving too slowly for the module receiving them to use.
Degraded communication is more insidious than none at all. A silent module is obvious and the vehicle responds decisively; a module whose messages arrive intermittently corrupted produces behaviour that is merely odd, and odd behaviour gets driven around for months. Marginal grounds and corrosion cause this far more often than a failed module, because both raise resistance enough to distort signal edges without breaking the connection.
Likely causes
Start here
- Poor module ground connection · moderate
- Corroded transmission connector · moderate
- Damaged data bus wiring · specialist
Less common
- Low system voltage · 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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