- Disconnect the engine wiring harness from the ECT sensor.
- Connect an ohmmeter between the 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.
- Once again, disconnect the engine wiring harness from the ECT sensor.
- Measure and note the ECT sensor resistance with the engine hot.
- Compare the cold and hot ECT sensor resistance measurements with the accompanying chart.
- If readings do not approximate those in the chart, the sensor may be faulty.
- Check the appropriate fuse before attempting any other diagnostics.
Disconnect the sending unit electrical harness.
CAUTIONNever open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.
- Remove the radiator cap and place a mechanic-s thermometer in the coolant.
- Using an ohmmeter, check the resistance between the sending unit terminals.
Resistance should be high (74 ohms) with engine coolant cold and low (9.7 ohms) with engine coolant hot.
NOTEIt is best to check resistance with the engine cool, then start the engine and watch the resistance change as the engine warms.
- If resistance does not drop as engine temperature rises, the sending unit is faulty.
If the PCM receives a high engine temperature signal from the ECT, it adjusts fueling rates to protect the engine from damage due to overheating.
Checking the ECT sensor voltage versus resistance:
Disconnect the ECT sensor connector.