P0865: TCM Communication Circuit Low
MediumPowertrainTransmission
What does P0865 mean?
P0865 is a diagnostic trouble code indicating "TCM Communication Circuit Low". The ECU is detecting a voltage reading that is below the expected range in the transmission circuit. This typically points to a wiring short, a faulty sensor, or a grounding issue.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Intermittent warning lights
- Erratic gauge readings
Estimated repair cost
Typical range in Australia (parts + labour)
$100 – $500 AUD
Common causes
- Damaged or corroded wiring harness
- Loose or disconnected electrical connector
- Failed transmission sensor or actuator
- Blown fuse in the related circuit
- Poor ground connection
What should you do?
This code sits in a powertrain control module. The engine or transmission can drop into limp mode or cut out, which is its own hazard in traffic or on a motorway. Get it diagnosed before your next trip rather than waiting for the next service.
Get a diagnosis for YOUR car
Code P0865 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.