RX300 1999

Engine Coolant Temperature Sensor

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Location



Specific to:

Lexus RX300 1999-2003



Click image to see an enlarged view

Fig. ECT sensor location-RX300

Operation



Specific to:

Lexus RX300 1999-2003

Lexus RX330 2004-2006

The Engine Coolant Temperature (ECT) Sensor is a Negative Temperature Coefficient (NTC) Thermistor that monitors the engine coolant temperature. The ECT Sensor operates within a 5 volt DC reference range, and provides a linear input signal to the Powertrain Control Module (PCM) that is based upon the measured engine coolant temperature. The PCM uses data from the ECT Sensor to calculate Air-Fuel mixture, ignition timing, and fuel injector pulse width. In some instances, the ECT signal is used to control the engine cooling fans and the operation of the air conditioning (A/C) system.

Removal & Installation



Specific to:

Lexus RX300 1999-2003

  1. Before servicing the vehicle, refer to the Precautions Section.
    NOTE
    If working near and/or around the SRS system and components, be sure to disable the SRS system.

  2.  
  3. Disconnect the negative battery cable.
    NOTE
    When disconnecting the cable be sure that the ignition switch and headlight switches are off.


    NOTE
    When disconnecting the cable, certain systems will have to be initialized after reconnecting the cable. These systems are adaptive front lighting system, power window control system, power back door system, SRS system, audio system, sliding roof system and certain DTC codes. Be sure to write down any important information before disconnecting the cable. The Toyota scan tool, or equivalent, must be used. Follow the directions on the appropriate scan tool to complete initialization procedure.

  4.  
  5. Drain the engine coolant. Be sure to properly dispose of used coolant.
  6.  
  7. Remove the necessary components in order to gain access to the sensor.
  8.  
  9. Disconnect the electrical connector.
  10.  
  11. Remove the sensor from its mounting.
  12.  
  13. Discard the gasket.

    Click image to see an enlarged view

    Fig. ECT sensor and related components-RX300

  14.  

To install:


NOTE
Be sure to use new fasteners, as required.

  1. Using a new gasket install the sensor to its mounting.
  2.  
  3. Tighten the sensor to 14 ft. lbs.
  4.  
  5. Install the electrical connector.
  6.  
  7. Continue the installation in the reverse order of the removal procedure.
  8.  
  9. Be sure to fill the cooling system with the proper grade and type engine coolant.
  10.  
  11. Start the engine and check for leaks, correct as required.
  12.  

Testing



Specific to:

Lexus RX300 1999-2003

  1. Drain engine coolant.
  2.  
  3. Disconnect the ECT sensor connector.
  4.  
  5. Using a 19 mm deep socket wrench, remove the ECT sensor and gasket.
  6.  
  7. Using an ohmmeter, measure the resistance between the terminals.
  8.  
  9. If the resistance is not as specified, replace the ECT sensor.

    Click image to see an enlarged view

    Fig. ECT testing

  10.  

To install:

  1. Install a new gasket to the ECT sensor.
  2.  
  3. Using a 19 mm deep socket, install the ECT sensor. Tighten to 14 ft. lbs. (20 Nm).
  4.  
  5. Connect the ECT sensor connector.
  6.  
  7. Refill with engine coolant.
  8.  

 
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