P0866
TCM Communication Circuit High
P0866 is an OBD-II diagnostic trouble code meaning: TCM Communication Circuit High. Common causes: short circuit in tcm communication circuit, tcm module malfunction. Estimated repair cost: $56–278.
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
Error P0866 by Vehicle Brand
FAQ
What does the P0866 code mean?
P0866 is an OBD-II diagnostic trouble code that indicates: TCM Communication Circuit High
What causes a P0866 error code?
The most common causes of P0866 include: Short circuit in TCM communication circuit; TCM module malfunction; Problems with wiring or connectors; Short circuit to ground.
How do I fix a P0866 diagnostic trouble code?
To fix P0866: 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. For a complete diagnosis, use an OBD-II scanner.
Is it safe to drive with P0866?
Do not drive — repair immediately
How much does it cost to fix P0866?
The estimated repair cost for P0866 is $56–278. Actual cost depends on your vehicle, location, and labor rates.
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