PowertrainP0866
CautionSeverity: Caution - get it checked when you can
TCM Communication Circuit High
Key terms: SAE J2012: the standard generic code list · Powertrain: engine, transmission and emissions
1What it means in plain English
This range normally covers the transmission control system, but some manufacturers use P07-P09 codes for unrelated functions (fuel pump control, air-mix motors, lighting or windows). Check the description before assuming it is a transmission fault.
2Common causes
- Low or dirty transmission fluid
- Faulty shift solenoid
- Faulty speed sensor
- Wiring or connector fault
- Internal transmission wear
3Can I drive?
If the transmission slips, jerks, will not shift, or a transmission temperature warning is on, stop driving and let it cool: continuing can cause expensive damage. If the code names a different system (for example the fuel pump), treat it on its own terms; a fuel-pump control failure can stall the car, so have it checked before driving further. Otherwise drive gently to a workshop.
This page gives general information. It is not professional advice. For a definite diagnosis and a repair quote, ask a qualified mechanic to inspect the car.
4Brand data 23
| Brand | Code | Description | System |
|---|---|---|---|
| Ashok Leyland CV | P0866 | MDP Minimum Absolute - Injector1 Brand | Powertrain |
| BAIC Motor | P0866 | TCM Communication Circuit High Brand | Powertrain |
| BYD | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Chery | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Daewoo | P0866 | TCM Communication Circuit High Brand | Powertrain |
| DFFS | P0866 | TCM Communication Circuit High Brand | Powertrain |
| DFFX | P0866 | TCM Communication Circuit High Brand | Powertrain |
| DFXK | P0866 | TCM Communication Circuit High Brand | Powertrain |
| EOBD | P0866 | TCM sideahel kõrge Brand | Powertrain |
| Geely | P0866 | TCM Communication Circuit High Brand | Powertrain |
| GM | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Great Wall | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Hafei | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Hyundai | P0866 | TCM Communication Circuit High SAE | Powertrain |
| Isuzu | P0866 | TCM Communication Circuit High SAE | Powertrain |
| Land Rover | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Peugeot | P0866 | TCM Communication Circuit High SAE | Powertrain |
| Saab | P0866 | TCM Communication Circuit High Brand | Powertrain |
| MG (SAIC) | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Subaru | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Tata | P0866 | TCM Communication Circuit High Brand | Powertrain |
| Toyota | P0866 | TCM communication circuit high Brand | Powertrain |
| Volkswagen | P0866 | SAE: TCM Communication Circuit: High Brand | Powertrain |
Legend: SAE is the generic J2012 description; Brand is text taken from that manufacturer’s data. Manufacturer rows keep the wording and language of the source data, and non-English text is tagged so screen readers pronounce it correctly.
5Related codes
Browse Pxxx codes or P086xx codes.