ION, L-Series, S-Series 1999-2005

Testing

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NOTE
The sensor is threaded into the coolant passage in the back of the cylinder head.

  1. Unplug the connector from the sensor and use the chart to check the sensor resistance with an ohmmeter. This can also work if the sensor is removed and immersed in a container of water.
  2.  
  3. With the ignition switch ON , there should be some voltage across the connector terminals. If not, check the wiring between the sensor and the PCM.
  4.  
  5. If using a scan tool, the reading should be the same as the actual coolant temperature with the ignition switch ON .
    1. If the reading is less than -32°F (-35°C), unplug the sensor connector and jumper the PCM circuit terminals together. If the reading goes to above 266°F (130°C), the problem is in the PCM connector, ground or in the sensor. If the reading does not change or go high enough, the problem is in the wiring or the PCM.
    2.  
    3. If the reading is more than 284°F (140°C), unplug the sensor connector. If the reading goes below -32°F (-35°C), the problem is in the sensor. If it does not change or does not go low enough, the problem is in the wiring or the PCM.
    4.  

  6.  
  7. If a scan tool is available, allow the engine too cool to the ambient temperature overnight, then compare the CTS and the ATS readings. Temperatures should be within 4 degrees of each other with the ignition ON and the engine not running.
  8.  

  1. Check the condition of the connector. Make sure the connector is firmly attached. Check for broken or bent connector pins. Repair any connector damage before continuing with troubleshooting the issue.
  2.  
  3. Check the condition of the wiring to the connector. If the wiring is damaged, repair the wiring before continuing with any further tests.
    NOTE
    The sensor is threaded into the coolant passage in the back of the cylinder head.

  4.  
  5. Unplug the connector from the sensor and use the chart to check the sensor resistance with an ohmmeter. This can also work if the sensor is removed and immersed in a container of water.
  6.  
  7. Remove the coolant temperature sensor.
  8.  
  9. Place the sensor in a container of water with a temperature approximately 20 degrees C (68 F).
  10.  
  11. Using an ohmmeter, check resistance between the terminals. The resistance should be 3520 ohms.
  12.  
  13. Raise the temperature of the container of water to approximately 80 degrees C (176F).
  14.  
  15. Using an ohmmeter, check resistance between the terminals. The resistance should be 332 ohms.
  16.  
  17. If the resistance is not as specified, replace the sensor.

    Click image to see an enlarged view

    Fig. Engine Coolant Temperature (ECT) sensor terminals; (1) Low reference, (2) ECT sensor signal



    Click image to see an enlarged view

    Fig. Temperature versus resistance chart

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