Coolant Temperature Sensor/Switch (For Computer): Description and Operation

PURPOSE
The sensor element extends into the coolant passage where it maintains constant contact with the engine coolant. The Powertrain Control Module (PCM) uses this sensor to measure the temperature of engine coolant.

OPERATION
The PCM sends out a reference voltage of approximately five (5) volts to the coolant temperature sensor. As coolant temperature changes, the internal resistance of the sensor will change, causing a varying voltage drop across the sensor. The PCM reads the voltage drop across the sensor as engine coolant temperature.

Based on the amount of voltage drop at the coolant sensor, the PCM will, adjust the fuel injector pulse width (a cold engine will receive a longer pulse width, allowing for a richer mixture), compensate for condensation of fuel in the intake manifold, monitor and adjust engine warm-up speed, advance ignition timing when the engine is cold, and activate the Electric EGR Transducer (EET) to prevent vacuum from reaching the EGR valve.

CIRCUIT OPERATION
The engine coolant temperature sensor provides an input to the Powertrain Control Module (PCM) on circuit K2. This sensor input is also used for the instrument cluster coolant temperature gauge. Description and Operation

From circuit K2, the engine coolant temperature sensor draws up to 5 Volts from the PCM. The sensor is a variable resistor. As coolant temperature changes the resistance in the sensor changes, causing a change in current draw. The K2 circuit connects to cavity 26 of the PCM connector. The PCM provides a ground for the engine coolant temperature sensor signal (circuit K2) through circuit K4. Circuit K4 connects to cavity 43 of the PCM.