Coolant Temperature Sensor

Coolant Temperature Sensor

Coolant Temperature Sensor




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.


See Figures 1 through 5

Fig. Fig. 1: Unplug the ECT sensor to access the sensor

Fig. Fig. 2: Test the resistance of the ECT sensor across the two sensor pins

Fig. Fig. 3: Another method of testing the ECT is to submerge it in cold or hot water and check resistance

Fig. Fig. 4: The ECT can be monitored with an appropriate and Data-stream capable scan tool

Fig. Fig. 5: ECT and IAT resistance-to-temperature specifications

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


See Figures 6 through 20

Fig. Fig. 6: Grasp and unfasten the retaining clips ...

Fig. Fig. 7: ... located in the following positions -2.0L engine, 2.5L similar

Click image to see an enlarged view

Fig. Fig. 8: The MAF connector is released by pressing down on the retaining spring-shown here already disconnected

Fig. Fig. 9: Label and disconnect the MAF sensor ...

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Fig. Fig. 10: ... and the IAT sensor

Fig. Fig. 11: Loosen the clamp on the air cleaner tube

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Fig. Fig. 12: Lift the air cleaner inlet tube slightly and slide the retaining tab on the air intake resonator out and ...

Fig. Fig. 13: ... remove the air cleaner inlet tube from the vehicle

Fig. Fig. 14: ECT sensor mounting-2.5L engine

Click image to see an enlarged view

Fig. Fig. 15: Place a suitable size socket over the sensor. A special socket used for sensors, as shown here, can be used but is not necessary

Fig. Fig. 16: Carefully loosen the sensor from the plastic thermostat housing

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Fig. Fig. 17: When loosened, remove the ECT sensor from the thermostat housing

Fig. Fig. 18: Use a quality thread sealant to ...

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Fig. Fig. 19: ... coat the threads of the ECT sensor before installation

Fig. Fig. 20: The ECT sensor must be tightened with a torque wrench to specifications or the plastic thermostat housing can crack

  1. Disconnect the negative battery cable.
  2. Drain and recycle the engine coolant.


Never 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.

  1. On the 2.0L engine, remove the air intake resonators.
  2. On the 2.5L engine, raise and support the vehicle.
  3. Disconnect the ECT sensor connector.
  4. Remove the ECT sensor from the thermostat housing (2.0L) or the water crossover tube (2.5L).

To install:

  1. Coat the sensor threads with Teflon® sealant.
  2. Thread the sensor into position and tighten to 10-14 ft lbs. (14-19 Nm) on the 2.5L engine and 89-120 inch lbs. (10-14 Nm) on the 2.0L engine.
  3. Attach the ECT sensor connector.
  4. On the 2.0L engine, install the air intake resonators.
  5. On the 2.5L engine, lower the vehicle.
  6. Connect the negative battery cable.
  7. Refill the engine cooling system.
  8. Start the engine and check for coolant leaks.
  9. Bleed the cooling system.