Audi Cars 1999-05

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Testing



Engine Coolant Temperature Gauge

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).

Multiple Wire Sensors

NOTE
On some models, terminal 2 (ground) is brown, and terminal 4 (signal) is blue/white. On other models, 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 ) could be brown/green on 1995-96 2.0L vehicles and can easily be confused with terminal 2 on 1.8, VR6 and V6 models, 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. Check the fuses and replace as necessary.
  2.  
  3. With the ignition switch OFF , disconnect the electrical connector from the gauge sending unit.
  4.  
  5. On 1994 and later models with the 4-wire electrical connector, locate the electrical terminals 2 and 4 of the electrical connector (refer to the illustration provided). Typically the terminal 2 is a blue wire with a brown tracer and terminal 4 is a brown wire, however this may differ from year to year and model to model.
  6.  
  7. With the ignition switch OFF , disconnect the harness connector from the sensor.
  8.  
  9. On 1995-96 2.0L ABA engines:
  10.  
    1. Using a multimeter, verify that terminal 2 is grounded.
    2.  
    3. If continuity does not exist between terminal 2 and ground, use the wiring diagrams to verify, trace and repair any damaged wiring. For additional information, please refer to the following topic(s): Chassis Electrical, Wiring Diagrams.
    4.  
    5. Set the multimeter to the DC voltage, and connect the test leads between terminal 4 and ground.
    6.  
    7. Turn the ignition switch ON and verify that voltage (approximately 5 volts) exists between terminals 4 and ground.
    8.  
    9. If voltage does not exist between terminal 4 and ground, use the wiring diagrams to verify, trace and repair any damaged wiring. For additional information, please refer to the following topic(s): Chassis Electrical, Wiring Diagrams.
    10.  

  11. On 1.8L, VR6 and V6 engines, the coolant temperature gauge sensor terminals are 2 (signal from gauge) which is typically a blue/white or black/brown wire, and terminal 4 (ground) which is typically brown.
  12.  


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 to verify, trace and repair any damaged wiring. For additional information, please refer to the following topic(s): Chassis Electrical, Wiring Diagrams.
  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 to verify, trace and repair any damaged wiring. For additional information, please refer to the following topic(s): Chassis Electrical, Wiring Diagrams.
  12.  

  1. If both terminal circuits are in proper working order, and the coolant temperature gauge does not work properly, check the function of the sensor as follows:
  2.  

Obtain the listed resistors to achieve the following gauge results:



110 Ohms: Temperature gauge should read 194°F (90°C)
 
50 Ohms: Temperature gauge should read 248°F (120°C))
 


CAUTION
Failure to correctly identify and probe the correct terminals of the 4-wire electrical connector may cause severe damage to the control unit or other electrical components.

  1. Turn the ignition switch to the OFF position.
  2.  
  3. Connect one of the 2 resistors in series with 2 suitable electrical probes attached to terminals 2 and 4 .
  4.  


CAUTION
Do NOT force a test probe into the electrical connector. When using an electrical probe use care to not damage the connector. If an electrical connector is damaged it should be replaced.

  1. Turn the ignition switch to the ON position for a brief moment and monitor the operation of the engine coolant gauge. The coolant temperature gauge should register as outlined above.
  2.  
  3. If the gauge reads correctly, replace the sensor. If the gauge does not register, check for a blown fuse, an open circuit, a damaged or shorted wire, electrical connector or a faulty gauge.
  4.  
  5. For verification purposes, if necessary, test the sensor.
  6.  

Single Wire Sensors
  1. Check the fuses and replace as necessary.
  2.  
  3. With the ignition switch OFF , disconnect the electrical connector from the gauge sending unit.
  4.  
  5. On models with a single wire coolant sensor, typically a yellow wire with a red tracer, connect the wire for the temperature sensor electrical connector to one of the leads of an 80-ohm resistor. Ground the other lead of the 80-ohm resistor to a known good chassis ground.
  6.  
  7. Turn the ignition switch to the ON position for a brief moment. The gauge should read hot, or 230°F (110°C).
  8.  
  9. Repeat the above steps using a 50-ohm resistor. When the ignition is switched to the ON position for a brief moment, the gauge should reach the warning zone and the overheat indicator light should blink.
  10.  
  11. If the gauge operates correctly, replace the sensor. If the gauge does not register, check for a damaged or shorted wire, electrical connector or a faulty gauge.
  12.  

 
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