Description And Operation - Engine Coolant Temperature (ECT) Sensor

The Powertrain Control Module (PCM) monitors the ECT Sensor analog signal voltage. The ECT Sensor input signal is used with other sensor inputs in calculating fuel delivery and engine timing. The PCM also uses the ECT Sensor input for determining when to enable several OBD diagnostics. Each of these will impact emissions, which is why the ECT Sensor signal must be rationalized by the PCM.

The ECT Sensor rationality diagnostic looks at the outputs of three temperature sensors and compares them under cold start conditions. Following a start to run delay time the outputs of the Ambient Air Temperature (AAT) Sensor, Engine Coolant Temperature (ECT) Sensor, and Intake Air Temperature (IAT) Sensor will be compared. If the IAT and AAT Sensors agree and the coolant temperature does not agree, the ECT Sensor is declared as irrational. If declared irrational a second comparison will be done after a short drive cycle.