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

The temperature sensor is located in the intake manifold between the intake manifolds of cylinders 3 and 4 and is in contact with the engine coolant. The sensor is of the NTC type.

The engine control module measures the coolant temperature by applying 5 V to the sensor from pin 68 via an integral 2.74 kohm resistor. The sensor is grounded via pin 67.

The ECM receives reference ground from the sensor ground lead to pin 66 to obtain a precise temperature measurement. The voltage across the resistor in the ECM is proportional to the coolant temperature.

The value is used to determine the fuel injection time in pre-injection and for cold starting and to produce a richer fuel/air mixture during warming-up. The activation of closed loop and idling speed also depends on the engine coolant temperature.

In the event of sensor failure or a break in the circuit, the engine control module will set a default temperature that is equivalent to the intake air temperature on starting and then incremented by 1 °C (1.8 °F) every 150th engine revolution.