Theory Of Operation

Engine Coolant Temperature (ECT) Sensor performance 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, engine coolant and intake air temperature sensors will be compared. If the Intake Air and Ambient Air Temperature Sensors agree and the engine 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. The ECT Sensor is a variable resistor that functions as a normal two wire 5-Volt Sensor. The PCM supplies a 5-volt reference and a ground to the sensors low reference signal circuit.