Code Definition

P0668 — ECM/TCM internal Temperature sensor circuit low

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

About P0668

P0668 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.

When P0668 is stored, the module has detected a signal or supply voltage lower than the expected operating range; and a sensor-related fault — the reported value from the named sensor is out of spec.

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 P0668 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 P0668 is set when the Engine Control Module (ECM) or Transmission Control Module (TCM) detects a low voltage condition in the circuit of its internal temperature sensor. This indicates that the voltage in the temperature sensor circuit is below the expected threshold, potentially pointing to issues like a partial short to ground, a fault in the sensor itself, or a problem with the wiring or connectors. The internal temperature sensor in the ECM or TCM is critical for monitoring the module's operating temperature, ensuring it remains within safe limits. A low voltage in this circ...

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