Theory Of Operation

The cooling system of the modern internal combustion engine has two main functions. The first function is to keep the engine from overheating once the engine is at operating temperatures. This is achieved by keeping the cylinder head cool to eliminate pre-ignition and the cylinder block warmer for decreased friction. The secondary function is to increase the engine temperature rapidly to eliminate high friction at cold temperatures and increase cabin heat, more rapidly, for the vehicle occupant comfort. The temperature of the coolant fluid is monitored by the Powertrain Control Module(PCM) using the engine coolant temperature sensor. The PCM checks rationality of this data by comparing the received data to other temperature sensors on the engine, such as the Engine Oil Temperature (EOT) sensor.

The Engine Coolant Temperature (ECT) Sensor operates as a typical two wire sensor. It receives a 5-Volt signal on the ECT Sensor Signal circuit and is grounded through the Coolant Temperature Sensor Return circuit. It acts as a variable resistor, and changes resistance as temperature changes.