Theory Of Operation

This diagnostic is used to detect an Engine Coolant Temperature (ECT) Sensor that is in range but reading incorrectly. Unlike the temperature sensor performance diagnostic that runs only on cold starts and compares all of the temperature sensor values, this diagnostic runs continuously. The Powertrain Control Module (PCM) models a predicted ECT Sensor value and compares that model to the actual ECT Sensor. If the difference is too large, a counter starts to increment. When the counter reaches a calibrated threshold, a fault is set.