Audi Cars 1999-05

Testing 1

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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


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  


WARNING
The cooling system is under pressure. There is a danger of scalding when opening!


NOTE
Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor.

  1. Connect the vehicle to the diagnosis and service system.
  2.  
  3. Switch the ignition on.
  4.  
  5. Under address word "33 - On Board Diagnostic (OBD)", select "Diagnostic mode 1: Check measured values" .
  6.  
  7. Select measured value "PID 05: Coolant temperature" .
  8.  
  9. Check the specified value of the coolant temperature:
  10.  
  11. If specified value is not obtained, continue test according to the following results:

    If the temperature indicated is approximately minus 40 degrees Celsius, there is an open circuit or a short to the battery.
     
    If the temperature indicated is approximately 140 degrees Celsius, there is an short circuit to the ground.
     

  12.  
  13. If the specified value is obtained, start the engine and let it run at idle.
  14.  
  15. Temperature value must increase uniformly in increments of 1.0 degrees C.
  16.  
  17. If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent. Replace Engine Coolant Temperature (ECT) Sensor.
  18.  

Sensor Installed In Vehicle



Testing the sensor in the vehicle requires the following:



An ohmmeter
 
Electrical test leads
 

  1. With a cold engine, measure the resistance at the sensor:
  2.  
    1. On single wire sensors, between the sensor terminal and ground.
    2.  
    3. On multiple wire sensors, between the terminals for the coolant temperature gauge.
    4.  

  3. Write the measurement down for future reference.
  4.  


NOTE
On sensors with 4-wire connectors, make sure to probe the proper electrical terminals.

  1. Reconnect the sensor electrical connector and start the engine. Allow the engine to run for approximately 5 minutes, then turn the engine OFF .
  2.  
  3. Detach the sensor electrical connector and recheck the resistance of the sensor.
  4.  
  5. The resistance should have decreased from the previous measurement.
  6.  
  7. Reconnect the sensor electrical connector and start the engine again. Allow the engine to run for approximately 5 minutes, then turn the engine OFF .
  8.  
  9. Detach the sensor electrical connector and recheck the resistance of the sensor.
  10.  
  11. The resistance should decrease from the previous measurement, until the coolant temperature reaches its normal operating temperature, at which time the resistance should stabilize. If the sensor's resistance does not change as the engine's coolant temperature changes, or should the sensor develop an intermittent open or closed circuit during testing, replace the sensor. To test the sensor for accuracy, the use of a suitable model Scan Tool or special factory-approved will be necessary. The sensor must be removed and tested alongside a known good sensor and the resistance values compared.
  12.  

Sensor Removed From Vehicle



Testing the sensor once it's removed from the vehicle requires the following:



An ohmmeter
 
A suitable hot plate
 
Electrical test leads
 
A safe working environment
 
Thermometer with a range of 30-212°F (-1-100°C)
 
A suitable pan capable of containing water and being heated safely to boiling; 212°F (100°C).
 

  1. With the probe of the sensor submerged in ice cold water, measure the resistance as follows:
  2.  
    1. On single wire sensors, between the sensor terminal and ground.
    2.  
    3. On multiple wire sensors, between the terminals for the coolant temperature gauge.
    4.  



NOTE
On sensors with 4-wire connectors, make sure to probe the proper electrical terminals.

  1. Write both the water temperature and sensor resistance down for future reference.
  2.  
  3. Begin heating the water. The resistance should decrease as the water temperature increases. If the resistance does not decrease, the sensor is defective and should be replaced.
  4.  
  5. To test the sensor for accuracy, monitor the water temperature and resistance change. As the temperature changes, so should the resistance. If at any time the sensor shows signs of an open circuit, erratic operation or no resistance at all, replace the sensor.
  6.  



Click image to see an enlarged view

Fig. When the sensor was placed in a cup of ice water, the resistance increased instantly

Testing If Display Approx. -40.0 Degrees C:





Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  



Click image to see an enlarged view

Fig. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Bridge terminals 1 and 2 of connector using adapter cables from connector test kit and observe indication on display.

    Click image to see an enlarged view

    Fig. Bridge terminals 1 and 2 of the connector using the adapter cables from the connector test kit and observe indication on display

  2.  
  3. If the indication jumps to approx. 140.0 degrees C, end diagnosis and switch ignition off. Replace Engine Coolant Temperature (ECT) Sensor.
    WARNING
    Cooling system is under pressure. Danger of scalding when opening!

  4.  
  5. If the indication remains at approx. -40.0 degrees C, end diagnosis, switch the ignition off and check the wires.
  6.  

Testing If Display Approx. 140.0 Degrees C:





Click image to see an enlarged view

Fig. Disconnect 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

  1. Disconnect the 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow).
  2.  
  3. If the indication jumps to approx. -40.0 degrees C, end diagnosis, switch the ignition off, and replace the Engine Coolant Temperature (ECT) sensor.
  4.  
  5. If the indication remains at approx. 140.0 degrees C, end diagnosis, switch the ignition off and check the wiring.
  6.  
  7. Connect the test box to the wiring harness of the Motronic Engine Control Module (ECM).
  8.  
  9. Check the wires between the test box and the 2-pin connector for open circuits.

    Terminal 1 and socket 10
     
    Terminal 2 and socket 14
     

  10.  
  11. Wire resistance: max. 1.5 ohms
  12.  
  13. Check the wires for short circuit to each other, to Battery (+) and Ground (GND).
  14.  
  15. Specified value: infinite ohms
  16.  
  17. If the wires are okay, use a multimeter and adapter cables from the connector test kit to measure the resistance at the connector to the Engine Coolant Temperature (ECT) Sensor terminals 1 and 2.

    Click image to see an enlarged view

    Fig. Check wires between test box and 2-pin connector for open circuit according to wiring diagram.

  18.  
  19. Area A: Resistance values for temperature range 0 to 50 degrees C.
  20.  
  21. Area B: Resistance values for temperature range 50 to 100 degrees C.

    Click image to see an enlarged view

    Fig. Resistance read-out examples

  22.  
  23. Read-out examples:
    1. 30 degrees C is in range A and corresponds to a resistance of 1.5 to 2.0 kohms
    2.  
    3. 80 degrees C is in range B and corresponds to a resistance of 275 to 375ohms
    4.  

  24.  
  25. If the resistance is not okay, replace Engine Coolant Temperature (ECT) Sensor.
  26.  
  27. If the wires and resistance values are okay, replace Motronic Engine Control Module (ECM).
  28.  



Click image to see an enlarged view

Fig. Disconnect 2-pin harness connector at Engine Coolant Temperature (ECT) Sensor (arrow)

 
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