The Engine Coolant Temperature (ECT) Sensor is a "thermistor", a sensor whose resistance changes in response to engine coolant temperature. The sensor resistance decreases as the coolant temperature increases, and increases as the coolant temperature decreases. This input signal is used by the PCM help determine the correct air-to-fuel ratio for the engine's operating temperature. The PCM controls the fuel mixture by controlling how long the electrically triggered fuel injectors stay open. If the ECT sensor is unplugged, the PCM senses a very high resistance, and the engine may start when cold, however as the engine's temperature increases, a rich running condition will cause the engine to loose power and stall.
See Figure 1
- Disconnect the engine wiring harness from the ECT sensor.
- Connect an ohmmeter between the two ECT sensor terminals.
- With the engine cold and the ignition switch in the OFF position, measure and note the ECT sensor resistance.
- Connect the engine wiring harness to the sensor.
- Start the engine and allow the engine to reach normal operating temperature.
- Once the engine has reached normal operating temperature, turn the engine OFF .
- Again, disconnect the engine wiring harness from the ECT sensor.
- Measure and note the ECT sensor resistance with the engine hot.
- The ECT sensor should have 5,000 ohms resistance when the engine coolant temperature is cold. The ECT sensor resistance should decrease as the engine temperature increases. At operating temperature the ECT sensor resistance should be 100-400 ohms.
- If readings are not close, the sensor may be faulty.
REMOVAL & INSTALLATION
- Disconnect the negative battery cable.
- Drain and recycle the engine coolant.
- Detach the ECT sensor connector.
- Remove the ECT sensor from the thermostat housing
- Coat the sensor threads with Teflon® sealant.
- Thread the sensor into position and tighten.
- Attach the ECT sensor connector.
- Connect the negative battery cable.
- Refill the engine cooling system.
- Start the engine and check for coolant leaks.
- Bleed the cooling system as necessary.