See Figures 1, 2 and 3
The coolant temperature sensor is a thermistor (a temperature controlled variable resistor with a range of -40°F to 265°F) mounted in the engine coolant stream. Engine controller uses the temperature input to adjust the fuel mixture slightly richer and raise the idle speed, until normal operating temperatures are reached. On all models, this sensor is also used to control the cooling (radiator) fan operation.
The PCM supplies 5.0 volts to the coolant temperature sensor. The sensor provides an input voltage to the PCM. As coolant temperature varies, the sensor resistance changes resulting in different input voltage to the PCM.
When the engine is cold, the PCM will demand slightly richer air/fuel mixtures and higher idle speeds until normal operating temperatures are reached.
See Figure 4
- Make certain that the engine is cool (i.e. has not been run for a