AutoZone 2010 Honda Civic SI 2.0L MFI DOHC 4cyl | Repair Guides | Engine Cooling | Coolant Temperature Sensor | Testing | AutoZone.com

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    Volkswagen Cars 2000-05

    Testing

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    Diagnosing the engine coolant temperature sensor should be done in a step-by-step systematic order to determine the cause of the problem. Using a process of elimination technique allows the system operation to be fully verified.


    WARNING
    When trouble shooting electrical components, always consult a wiring diagram for the particular year, make and model to ensure proper test equipment connection and diagnosis. Failure to use suitable test equipment and testing methods could permanently damage the electrical component(s).

    The engine coolant temperature gauge uses an Engine Coolant Temperature (ECT) Sensor that is a heat sensitive variable resistance grounding circuit to monitor the engine's coolant temperature.

    The coolant temperature information is conveyed to the instrument panel from the signal received from the ECT sensor. To test the sensor, the gauge and its related components, first test the gauge operation to verify the problem is not in the gauge or gauge wiring. To test the gauge and ECT operation, perform the following procedures.



    Click image to see an enlarged view

    Fig. The Engine Coolant Temperature (ECT) sensor resistance decreases as the coolant temperature increases as shown in this graph of the ECM coolant sensor

    1. With the ignition 'OFF', remove the electrical connector at the coolant temperature sensor.
    2.  
    3. With a suitable Digital Multimeter (DMM), measure the resistance between the 2 terminals of the coolant temperature sensor (terminals 1 and 3 on the 1.9L Turbo Diesel).
    4.  



    Click image to see an enlarged view

    Fig. ECT resistance chart

    Range 'A' shows the resistance values for the temperature range from 0-50°C (32-122°F), and range 'B' shows the values for the temperature range from 50-100°C (123-212°F).

    Examples of how to read the diagram:



    30°C (86°F) is in range A and corresponds to a resistance of 1,500-2,000 ohms.
     
    80°C (176°F) is in range B and corresponds to a resistance of 275-375 ohms
     

    If specified value is not obtained, replace Engine Coolant Temperature (ECT) sensor.

    1. If specified value is obtained, check wiring between ECT sensor and ECM.
    2.  
    3. Connect VAG 1598/19 test box to ECM harness connector.
    4.  
    5. Check wiring for continuity between terminal 3 of ECT sensor harness connector and engine Ground (GND). Maximum resistance is 1.5 ohms.
    6.  
    7. Check signal wire for continuity between ECT sensor harness connector terminal 1 and test box socket 16A . Maximum resistance is 1.5 ohms.
    8.  
    9. Check both wires for short circuit to each other.
    10.  
    11. If the specified values are not obtained, eliminate short or open circuit in wiring between ECT sensor and ECM connector or engine Ground (GND).
    12.  

    If wiring is OK and the ECT sensor is OK, replace the ECM.

    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 Section 4 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 Section 6 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 Section 6 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 Section 6 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 Section 6 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.  

    Digifont



    1. Unplug the sensor connector and use an ohmmeter to check sensor resistance:

      1.55°F (13°C)-3000-3800 ohms
       
      2.65°F (18°C)-2200-3000 ohms
       
      3.75°F (24°C)-1800-2500 ohms
       
      85°F (29°C)-1500-2100 ohms
       
      150°F (65°C)-400-550 ohms
       
      200°F (93°C)-200-270 ohms
       

    2.  

    Motronic



    1. Unplug the sensor connector and use an ohmmeter to check sensor resistance:

      55°F (13°C)-3000-3800 ohms
       
      65°F (18°C)-2200-3000 ohms
       
      75°F (24°C)-1800-2500 ohms
       
      85°F (29°C)-1500-2100 ohms
       
      150°F (65°C)-400-550 ohms
       
      200°F (93°C)-200-270 ohms
       

    2.  

     
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