Our automotive experts have put together the following information about the P0866 diagnostic trouble code. We've provided the common symptoms that occur when this code is set along with the frequent repairs that address the issues related to the P0866 code.

OBD II Fault Code

  • OBD II P0866

    OBD-II Code Transmission may not shift properly is defined as a TCM Communication Circuit High

    If the Transmission Control Module (TCM) cannot communicate with other modules or the engine control module (PCM) can not communicate with the PCM, code P0866 will be set.

    Transmission may not shift properly Symptoms

    • Increased fuel consumption
    • Transmission may not shift properly

    Common Problems That Trigger the P0866 Code

    • Transmission Control Module (TCM) failure
    • Wiring issue
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