The engine computer has an internal temperature sensor that's reading too low, like a broken thermometer stuck on cold. This prevents the PCM from properly managing fuel, ignition timing, and emissions based on actual engine heat.

The PCM monitors its internal temperature sensor to adjust fuel mixture, spark timing, and shift points. When voltage reads below the minimum threshold, the sensor circuit is shorted to ground or the sensor has failed. The ECU cannot trust temperature data and may default to a safe but inefficient operating mode.

Voltage & Parameter Thresholds