P0866

TCM Communication Circuit High

Severity

🔴 High

Can you drive?

Do not drive — repair immediately

Approx. repair cost

$56–278 (est.)

Symptoms

Transmission of the gearbox into emergency mode
Shift faults
The Check Engine light comes on
Reduced vehicle dynamics
Difficulties when shifting gears

Causes

Short circuit in TCM communication circuit
TCM module malfunction
Problems with wiring or connectors
Short circuit to ground
Another related module is faulty

How to Fix

Check the condition of the wiring and connectors in the TCM communication circuit
Check TCM circuit fuses
Use a diagnostic scanner to check the TCM
Check for short circuit in the circuit
Replace TCM if necessary

Related codes

P0865 P0867 P0870