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 ECM measures the engine coolant temperature by supplying the sensor with 5 V through a 2.74 kOhm resistor built into the ECM from pin 68. The sensor is grounded via ECM 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 lambda control and idling speed also depends on the engine coolant temperature.

If the sensor does not work or if there is an open circuit, the ECM sets a substitute temperature of 26°C and the malfunction indicator lamp in the main instrument lights up.