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    Volkswagen Golf/Jetta/Cabriole 1990-1999

    Coolant Temperature Gauge Sensor

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    Click image to see an enlarged view

    Fig. Remove the coolant temperature sensor

    The coolant temperature gauge sensor is a temperature-variable resistor, or thermistor. As coolant temperature increases, the resistance of the sensor decreases or decreases, depending on the type of sensor.

    A1 and A2 platforms use a different type of circuit that A3 vehicles. On A1 and A2 vehicles, the circuit is a "resistance to ground" type. A3 vehicles use a "variable voltage" type, where a voltage is supplied to the sensor. Because of the circuitry design on A3 vehicles, testing of the coolant temperature gauge is limited.

    TESTING



    A1 and A2 Platform
    1. Using the appropriate electrical testing equipment, ground the yellow/red wire on the coolant temperature sensor harness connector.
    2.  
    3. With the wire grounded, and the ignition switch in the ON position, the gauge in the instrument cluster should indicate that the vehicle is overheating.
    4.  
    5. If the gauge does not move, inspect the wiring that connects to the instrument cluster. If the wiring is intact, the gauge unit in the instrument cluster is faulty.
    6.  

    A3 Platform
    4 cylinder engines

    NOTE
    Because the sensor on 4 cylinder A3 platform vehicles is combined with the coolant temperature sensor for the ECM, a Diagnostic Trouble Code (DTC) may be set, causing the engine light to illuminate. Refer to for information on resetting the ECM.

    On all 1993 and later engines, the coolant temperature gauge sensor is integrated into the coolant temperature sensor for the ECM. The combination 4-pin sensor is located on the coolant outlet on the side of the cylinder head. On 1993-95 vehicles, terminal 2 (ground) is brown, and terminal 4 (signal) is blue/white. On 1996-99 vehicles, terminal 2 (ground) is brown/green, and terminal 4 (signal) is red/yellow.


    WARNING
    Use caution when identifying the coolant temperature sensor leads, as the signal for the ECM (terminal 3) is brown/green on 1993-95 vehicles and can easily be confused with terminal 2 on 1996-99 vehicles, which is also brown/green. If the test leads are incorrectly connected when checking the coolant temperature gauge sensor, the ECM may be damaged.

    1. With the ignition switch OFF , disconnect the harness connector from the sensor.
    2.  
    3. Using a multimeter, verify that terminal 2 is grounded.
    4.  
    5. If continuity does not exist between terminal 2 and ground, use the wiring diagrams in to trace and repair any damaged wiring.
    6.  
    7. Set the multimeter to the DC voltage, and connect the test leads between terminal 4 and ground.
    8.  
    9. Turn the ignition switch ON and verify that voltage (approximately 5 volts) exists between terminals 4 and ground.
    10.  
    11. If voltage does not exist between terminal 4 and ground, use the wiring diagrams in to trace and repair any damaged wiring.
    12.  
    13. If both terminals are in order, and the coolant temperature gauge does not work properly, check the function of the sensor as follows:
      1. Make sure the engine is cold .
      2.  
      3. Set the multimeter to the resistance setting, and connect the test leads to terminals 2 and 4.
      4.  
      5. Start the engine, and allow it to idle. As the engine warms, the resistance should change. This verifies that the sensor is changing resistance with coolant temperature, but does not guarantee that the sensor is working properly.
      6.  

    14.  
    15. When finished with testing, turn the engine OFF and reconnect the sensor harness.
    16.  

    VR6 engines only

    On VR6 (AAA) engines, the middle sensor (usually yellow in color) on the cooling elbow is the gauge sensor. As with the 4-cylinder engines, this 4-pin sensor is also a combination sensor, but the circuit is shared with the after-run coolant fan control.

    On VR6 engines, the coolant temperature gauge sensor terminals are 2 (signal) which is blue/white, and terminal 4 (ground) which is brown. On 1996-99 vehicles, terminal 4 is identified by a brown/green wire.


    NOTE
    Note that the polarity of sensor terminals 2 and 4 are the opposite of 4 cylinder engines.

    1. With the ignition switch OFF , disconnect the harness connector from the sensor.
    2.  
    3. Using a multimeter, verify that terminal 4 is grounded.
    4.  
    5. If continuity does not exist between terminal 4 and ground, use the wiring diagrams in to trace and repair any damaged wiring.
    6.  
    7. Set the multimeter to the DC voltage, and connect the test leads between terminal 2 and ground.
    8.  
    9. Turn the ignition switch ON and verify that voltage (approximately 5 volts) exists between terminals 2 and ground.
    10.  
    11. If voltage does not exist between terminal 2 and ground, use the wiring diagrams in to trace and repair any damaged wiring.
    12.  
    13. If both terminals are in order, and the coolant temperature gauge does not work properly, check the function of the sensor as follows:
      1. Make sure the engine is cold .
      2.  
      3. Set the multimeter to the resistance setting, and connect the test leads to terminals 2 and 4.
      4.  
      5. Start the engine, and allow it to idle. As the engine warms, the resistance should change. This verifies that the sensor is changing resistance with coolant temperature, but does not guarantee that the sensor is working properly.
      6.  

    14.  
    15. When finished with testing, turn the engine OFF and reconnect the sensor harness.
    16.  

    REMOVAL & INSTALLATION



    1. Drain the coolant until it is just below the level of the sensor.
    2.  
    3. Disconnect the harness connector from the sensor.
    4.  
    5. Remove the sensor retaining clip, and pull the sensor straight out of the housing.
    6.  

    To install:

    1. Install a new O-ring on the sensor.
    2.  
    3. Using a small amount of fresh coolant, lightly lubricate the O-ring, and push the sensor in the housing.
    4.  
    5. While pushing inward on the sensor, install the retaining clip.
    6.  
    7. Plug in the harness connector to the sensor.
    8.  
    9. Refill the cooling system as necessary.
    10.  

     
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