Engine Coolant Temperature Sensor

This week we pulled the engine coolant temperature sensor off the Series 60. It is located on the right side (passenger) toward the rear of the head and block. It is an NTC-type thermistor which measures engine coolant temperature by changing resistance (temperature goes up, resistance goes down) and sends a voltage signal back to the ECM, which uses the information, along with that from other sensors, to adjust to a wide variety of engine operating conditions.

The sensor can be tested by comparing ambient temperature to resistance. One could also heat up a small container of water, stick the sensor in and measure resistance as long as the temperature of the water is known.

Coolant temp sensor and specifications for temperature and resistance.

Coolant temp sensor.

My reflection:

Removal and testing of this sensor shouldn't be any big deal on a typical engine, what might present a problem is finding specifications for it. It took longer to find specifications (appreciation to our instructor for finding the correct ones) than it did to pull the sensor and make measurements.

The moral here? Sometimes the hardest part of the job isn't turning a wrench, it's finding information! Without information, we would have little idea what correct resistance values are at what temperatures, and be unable to reliably diagnose this sensor.