See Figure 1
Most engine functions are affected by the coolant temperature. Determining whether the engine is hot or cold is largely dependent on the temperature of the coolant. An accurate temperature signal to the PCM is supplied by the coolant temperature sensor or Engine Coolant Temperature (ECT) sensor. The coolant temperature sensor is a thermistor mounted in the engine coolant stream. A thermistor is an electrical device that varies its resistance in relation to changes in temperature. Low coolant temperature produces a high resistance and high coolant temperature produces low resistance. The PCM supplies a signal of 5 volts to the coolant temperature sensor through a resistor in the PCM and measures the voltage. The voltage will be high when the engine is cold and low when the engine is hot.
See Figure 2
- Remove the ECT sensor from the vehicle.
- Immerse the tip of the sensor in a container of water.
- Connect a digital ohmmeter to the two terminal of the sensor.
- Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the water. Refer to the accompanying resistance value chart.
- Repeat the test at two other temperature points, heating or cooling the water as necessary.
- If the sensor does not meet specifications, it must be replaced.
REMOVAL & INSTALLATION
See Figures 3, 4, 5, 6, 7 and 8
- Disconnect the negative battery cable.
- If necessary, raise and safely support the vehicle, then drain the cooling system into a suitable container, to a level below the ECT sensor.
- If raised, lower the vehicle.
- For the 3.8L engine, remove the rear air intake duct.
- For the 1993-96 5.7L engine, remove the air intake duct.
- Detach the electrical connector from the Engine Coolant Temperature (ECT) sensor.
- For the 1998 5.7L engine, remove the no. 1 spark plug wire from the spark plug.
- Carefully back out the ECT sensor. For the 3.8L engine, you must use a 19mm deep well socket and 6-inch extension to remove the sensor.
- Coat the threads of the sensor with a suitable sealer.
Install the coolant temperature sensor and tighten as follows:
- 3.4L engine: 10 ft. lbs. (13 Nm)
- 3.8L engine: 22 ft. lbs. (30 Nm)
- 5.7L engine: 17 ft. lbs. (23 Nm).
- For the 1998 5.7L engine, attach the no. 1 wire to the spark plug.
- Attach the electrical connector.
- For the 3.8L engine, install the rear air intake duct.
- Fill the cooling system as required.
- Connect the negative battery cable.
- Start the engine and check for leaks.