Code Definition

P0666 — ECM/TCM internal temperature signal error

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0666

P0666 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0666 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The fault code P0666 is set when the Engine Control Module (ECM) or Transmission Control Module (TCM) detects an error in the internal temperature signal. This code indicates a malfunction in the system responsible for monitoring the internal temperature of the ECM or TCM. These control modules are equipped with temperature sensors to ensure they operate within a safe temperature range. A signal error could mean the sensor is not accurately reading the temperature, or there is a communication issue within the module's circuitry. This fault can lead to improper functioning of the ECM or TCM, as...

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