What is the P0866 fault number? What is the Transmission Control Module Communication Circuit High fault code? How can you fix P0866 fault codes? What are the causes and symptoms of the P0866 error code?
What is the P0866 Fault code? What does it all mean?
The P0866 code can be defined as “Transmission Control Module (TCM) Communication Circuit High” . The transmission must be able to communicate with the TCM and a number of engine control modules (ECM/ECU) in order to work properly. Each module is preloaded with the required parameters to allow the vehicle’s operation. If the data stream from the ECM is not in accordance with the expectations, that is, if the communication circuit connecting the TCM to ECM has an excessively high level of voltage, malfunction code P0866 is triggered.
Modern vehicles include two dozen or so control modules that are interconnected by the CAN (Controller Area Network). The CAN bus system consists simply of thousands upon thousands of circuits, cables, and it’s job is to enable various sensors, switches, modules, and to exchange data.
The TCM gathers information such as speed sensor data, throttle position sensor, steering angle sensor, and many other sensors. It then transmits the information via the CAN bus to the ECM. The ECM uses these data to optimize engine performance, fuel consumption, and calculate shift point calculations.
At least one auxiliary control module closely related monitors all control modules. The auxiliary control module will detect a problem with the TCM and set a fault code. If the voltage signal that the TCM sends to the ECM or other control module is higher than the expected parameters, the ECM cannot manage gear shifts effectively. Code P0866 will be issued. This could be due to an electrical or mechanical problem.
The P0866 fault code can affect vehicles of all makes and models, including but not limited to Dodge, Honda, Volkswagen or Mazda, Audi, Mazda Volvo, Skoda Porsche, Mercedes-Benz, Subaru, and others.
What is the P0866 Fault Code?
Below are some reasons to set fault code P0866:
- – Broken, damaged, melted, corroded and/or loose cables or connectors in CAN bus systems
- – A defective speed sensor or transmission sensor
- – Mechanical transmission failure
- TCM/ECM that has a problem or requires a software upgrade (in most cases these two modules are combined and are known as PCM).
What are the P0866 Malfunction Code Symptoms
These symptoms may be present in vehicles with code P0866.
- – Illumination and control of the check engine light
- – The Transmission Fault Light comes on
- – Incorrect or delayed gear changes
- Transmission may not shift to all gears or one.
- – Overheating engine and gearbox
- – Smoke and strong odors from the gearbox
- – Higher fuel consumption
- – Set other transmission related fault code
- – ABS deactivation
- – Flashing the Traction Control Light
- – Slippery roads: No traction
- – Failure to operate the traction control system
- – The vehicle may enter safe mode, and the vehicle can only be restricted to a specific gear
How do I fix the P0866 fault code?
There are several repairs that can resolve the P0866 fault code.
- – Repair of damaged connectors and cables in the CAN bus network
- – Replacing a traction control module or switch
- – Reprogramming and replacement of the transmission control modules
- – Reprogramming and replacing the engine control module
- – Update TCM/ECM software
The most common cause of P0866 OBDII fault codes is either damaged cables or a damaged connector. Check the manufacturer technical service bulletins for updates and other issues. If no issues are found, the transmission controller module and engine control units should be investigated.
How serious is the P0866 Fault code?
Fault code 0866 should be taken seriously as the failure of one of the control modules directly impacts several other modules. If this code is not decoded you risk more damage or being stranded. It is important to diagnose your vehicle if it displays P0866.
