Fault codeP0864

MODERATE

TCM Communication Circuit Range/Performance

What this code means

TCM Communication Circuit Range/Performance.

P0864 is a generic code: it means the same thing on every make. P0864 belongs to family P08xx — Transmission (continued). Its page explains how to read a code and groups all its codes by part.

Type of fault

The signal stays within its electrical limits, but its value is not plausible: it does not match what the control unit expects given the other sensors. The sensor may be drifting with age, but it may also be faithfully measuring a real mechanical problem — a leak, a blockage, an air leak. Replacing the sensor without checking does not always clear the fault.

Gearbox control unit (TCM)

The gearbox control unit drives the solenoids and reads the gearbox sensors. It communicates with the engine control unit over the vehicle network and is fed by its own relay and fuse.

What you notice

The gearbox goes into limp mode, sometimes several warnings at once, shifts that do not happen.

How to check it

Check its fuses and relay, then the battery voltage and the grounds: a weak supply causes many of these faults. Then the connectors of the unit, which on some cars sits on the gearbox itself and suffers from heat and leaks.

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

How to read this code

PPowertrain
0standardised code
8Transmission (continued)
64P0864