GM Malibu/Cutlass 1997-2000

Engine Coolant Temperature (ECT) Sensor

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OPERATION



The Engine Coolant Temperature (ECT) sensor 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 provides a reference signal to the PCM, which indicates engine coolant temperature. The signal sent to the PCM by the ECT sensor helps the PCM to determine spark advance, EGR flow rate, air/fuel ratio, and engine temperature. The ECT also is used for temperature gauge operation by sending it's signal to the instrument cluster.

The ECT is a two wire sensor, a 5-volt reference signal is sent to the sensor and the signal return is based upon the change in the measured resistance due to temperature.

TESTING





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Fig. ECT and IAT sensor resistance value chart

  1. Disconnect the engine wiring harness from the ECT sensor.
  2.  


NOTE
Inspect ECT sensor connector and terminals for signs of coolant seepage or corrosion.

  1. Connect an ohmmeter between the ECT sensor terminals.
  2.  
  3. With the engine cold and the ignition switch in the OFF position, measure and note the ECT sensor resistance.
  4.  
  5. Connect the engine wiring harness to the sensor.
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  7. Start the engine and allow the engine to reach normal operating temperature.
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  9. Once the engine has reached normal operating temperature, turn the engine OFF .
  10.  
  11. Once again, disconnect the engine wiring harness from the ECT sensor.
  12.  
  13. Measure and note the ECT sensor resistance with the engine hot.
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  15. Compare the cold and hot ECT sensor resistance measurements with the accompanying chart.
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  17. If readings do not approximate those in the chart, the sensor may be faulty.
  18.  

REMOVAL & INSTALLATION





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Fig. The ECT sensor on the 2.4L engine is located on the coolant inlet at the upper radiator hose



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Fig. The ECT sensor on the 3.1L engine is located on the right side of the engine near the water inlet

  1. Disconnect the negative battery cable.
  2.  
  3. Drain and recycle the engine coolant.
  4.  
  5. On the 3.1L engine, remove the air cleaner outlet tube.
  6.  
  7. Unplug the ECT electrical connection.
  8.  
  9. Using an appropriate tool, loosen the ECT sensor and remove it from the engine.
  10.  

To install:

  1. Use a suitable thread sealant and apply it to only the threads of the ECT sensor.
  2.  
  3. Install the ECT sensor.
  4.  
  5. On the 2.4L engine, carefully tighten the sensor until it is fully driven; seated, not stripped. On the 3.1L engine, tighten the sensor to 17 ft. lbs. (23 Nm).
  6.  
  7. Attach the ECT sensor electrical connector.
  8.  
  9. Refill and bleed the cooling system.
  10.  
  11. On the 3.1L engine, reattach the air cleaner outlet tube.
  12.  
  13. Connect the negative battery cable.
  14.  
  15. Run the vehicle and check for leaks.
  16.  

 
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