Chrysler Full-Size Trucks 1997-2000 Repair Guide

Engine Coolant Temperature (ECT) Sensor

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OPERATION



The Engine Coolant Temperature (ECT) is located on or near the thermostat housing.

The ECT sensor's resistance changes in response to engine coolant temperature. The sensor resistance decreases as the coolant temperature increases, and vice-versa. 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, and air/fuel ratio.

Some vehicles may have two ECTs fitted: one for input to the PCM and the other for input to the coolant temperature gauge or warning light.



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Fig. ECT sensor location-2.5L engine



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Fig. ECT sensor location-3.9L, 5.2L, 5.9L engines. Thermostat housing removed for clarity



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Fig. Location of the ECT and temperature gauge sensors-early V-10 engine

TESTING



  1. Check for resistance across the sensor terminals. The use of an input-impedance (digital) VOM is recommended.
  2.  
  3. Resistance will vary with coolant temperature. Generally, resistance will be about 18kilo-ohms at 50ºF (10ºC), decreasing to about 600 ohms at operating temperature. If the measured resistance is at or near zero (shorted) or at or near infinity (open), replace the sensor.
  4.  
  5. Bring the engine up to or near operating temperature.
  6.  
  7. Disconnect the negative battery cable.
  8.  
  9. Unplug the connector on the sensor.
  10.  


NOTE
Be sure you are unplugging and checking the ECT, and not the temperature gauge sending unit; they are two different parts.

  1. Connect an ohmmeter across the sensor connectors and observe the reading over time as the engine cools.
  2.  
  3. As the engine cools the resistance in the sensor should increase slowly.
  4.  
  5. If it doesn't, replace the sensor.
  6.  
  7. If a scan tool is available, it can be used to check the sensor. Call up sensor voltage in the "live" mode. Start and run the engine observing the sensor voltage. It should decrease and increase smoothly as engine temperature increase and then decreases.
  8.  



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Fig. The coolant temperature sensor can be tested using the Auto Xray® or equivalent tool's data display feature



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Fig. The ECT sensor's electrical connector terminal identification: (1) BK/LB; (2) TN/BK



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Fig. ECT sensor circuit diagram

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  


CAUTION
NEVER open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant.

  1. Drain the engine coolant below the level of the thermostat housing.
  2.  
  3. Remove the air cleaner assembly if necessary for access to the sensor.
  4.  
  5. Remove the connector from the sensor. Vehicles with air conditioning may benefit if you fabricate an L-shaped hook tool from a wire coat hanger about 8 in. (203mm) long. Use the hook for removal rather than pulling on the wiring harness.
  6.  
  7. Remove the sensor from the intake manifold.
  8.  

To install:

  1. Install the sensor in the manifold and tighten to 8 ft. lbs. (11 Nm).
  2.  
  3. Install the connector on the sensor. There is no polarity: the connector cannot be accidentally reversed.
  4.  
  5. Connect the negative battery cable.
  6.  
  7. Inspect for leaks.
  8.  
  9. Install the engine cover.
  10.  

 
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