All models use a water temperature sensor input, to provide an accurate temperature signal to the ECM. The sensor screws into a coolant passage in the engine and detect changes in engine temperature. The coolant temperature sensor is a primary input in determining the duty cycle, as well as engaging closed loop operation.
Some systems also use an air temperature sensor, located in the air cleaner housing. Both sensors are used to control various emission control devices.
The coolant and air temperature sensing units, use a thermistor which is sensitive to the changes in temperature. Electrical resistance of the thermistor decreases in response to the temperature rise. This change will cause a change in voltage on the sensor reference line. The ECM will use the reference line voltage to determine engine temperature.
See Figures 1 and 2
- Disconnect ECM 20 pin connector from control unit.
Measure the sensor resistance as follows:
Coolant temperature sensor-between terminal 8 and 19 of ECM 20 pin connector.
Compare the readings to the resistance chart and proceed as follows:
If both resistances are within specification, check/replace ECM control unit.
Remove and check the appropriate temperature sensor and measure the resistance across the terminals.
If temperature sensor is not within specification, replace sensor.
REMOVAL & INSTALLATION
Water Temperature Sensor
- Drain the engine coolant.
- Disconnect the harness connector.
- Using the correct size wrench, remove the sensor.
- Coat the threads of the new sensor with an approved anti-seize compound.
- Install the new sensor using the correct size wrench.
- Reconnect ECT harness connector.
- Refill the engine coolant.
- Run the engine until the cooling fans operate and check for leaks.