P0866 – TCM Communication High

Description

The ECM detects a high voltage condition in the TCM communication circuit.

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Symptoms

  • Harsh shifting
  • Limp mode
  • Warning lights

Causes

  • Open circuit
  • TCM failure
  • Wiring issues

Diagnosis

  • Monitor CAN voltage
  • Inspect wiring
  • Check grounds

Repair

  • Repair wiring
  • Replace TCM