Engine Temperature Sensor: Description and Operation

Coolant Temperature Sensor:

The Coolant Temperature Sensor, located near the carburetor, is a thermistor which relays an engine coolant temperature signal to the ECM. Temperature changes cause resistance through the sensor to vary, thus creating a signal the ECM can interpret. This signal is used as one of the criteria to determine when the system is ready to enter closed loop mode. The information is also used to modify the open loop duty cycle.

The temperature/resistance relationship is as follows:

Coolant Temp. Resistance

15°C (59°F) 4450 +293 or -336 ohms

20°C (68°F) 2100 - 2900 ohms

128°C (262°F) 80 +4.0 or -2.3 ohms