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

Fig. 5 Coolant & charge temperature sensors:

The coolant temperature sensor, Fig. 5, is mounted in the thermostat housing and allows the SMEC to monitor engine operating temperature in order to provide proper air/fuel mixtures. The sensor provides a variable resistance which is proportional to coolant temperature. When the engine is cold and sensor resistance is low, the SMEC provides richer air/fuel mixtures and increases engine idle speed to provide acceptable cold engine performance and allow quick warm up. When coolant temperature and sensor resistance increase, the SMEC provides leaner air/fuel mixtures and lowers engine idle speed to provide proper exhaust emission control and increased fuel economy.