P0668 PCM/ECM/TCM Internal Temperature Sensor Circuit Low

P0668 points to a low condition in the PCM, ECM, or TCM internal temperature sensor circuit. The module reports a temperature signal below its expected range.

Code details

Generic OBD-II · P0

System: Computer
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the module until power, ground, connector integrity, and low-voltage causes have been ruled out.

Symptoms of P0668

Check-engine light, sometimes with several unrelated codes at once.
Warning lights, a no-start, or intermittent electrical faults.
Communication or module-reset problems on a scan tool.

Common causes of P0668

Low battery voltage, poor grounds, corroded connectors, or blown fuses.
Wiring or network (CAN bus) faults between modules.
A module software/programming issue, or rarely a failed controller.

Useful checks before replacing parts

Review internal module temperature data, ambient temperature, battery voltage, freeze-frame conditions, controller grounds, and companion internal fault codes.
Inspect module connectors for moisture, corrosion, pin fit issues, low supply voltage, weak grounds, and harness faults that could bias the sensor low.
Confirm whether the temperature value is stuck low both cold and hot before deciding the fault is internal to the module.

Related OBD-II codes

These nearby computer entries can help compare wording and pin down the fault area.