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

Coolant Temperature Sensor:

This sensor is located in the intake manifold, and is in the flow of engine coolant so that it can monitor the coolant temperature. This sensor is a variable resistor whose resistance value is inversely proportional to the temperature of the engine (as the temperature of the engine increases, the resistance value decreases).

The ECU monitors the voltage levels that are returned from the coolant temperature sensor. As the coolant temperature varies, so will the voltages being returned to the ECU. The ECU interprets these voltage levels to indicate one of many different scenarios possible, and once it receives these signals it will do one or more of the following:

- Control engine warm-up idle speed.
- Increase the ignition advance when the engine is warming up.
- Adjust the injector pulse width for the appropriate engine operating condition. The ECU will increase the injector pulse width when the coolant temperature is cold resulting in a richer air-fuel mixture.
- Adjust for fuel condensation (puddling) in the intake manifold.
- Energize the EGR valve solenoid so that no EGR can occur while the engine is warming up or at idle.