Coolant Temperature Sensor (CTS)

The coolant temperature sensor is located in thermostat housing. It is a variable resistor (thermistor) type sensor, and transmits an electrical signal to the ECM proportionate to engine temperature. A low coolant temperature produces a high resistance while a high coolant temperature produces a low resistance.

The ECM supplies a 5-volt signal to the coolant temperature sensor and measures the voltage that returns. By measuring the voltage drop between the 2 readings, the ECM is informed of engine coolant temperature. Coolant temperature is used for fuel management, idle air control, spark timing, EGR operation, canister purge operation and other engine operating functions.