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Circuit Test B1 - Vane Air Temperature (Vat)

Fig 1: VAT Circuits
G108493
NOTE: Enter this test only when a Code 10 is displayed during the QUICK TEST procedure or when directed here from another CIRCUIT TEST. To prevent replacement of good components, be aware that the following non-EEC items may be faulty: ambient temperature too low or too high. Ambient temperature must be greater than 50°F (10°C) for this test. This test is intended to diagnose only the following: VAT sensor, VAT and Signal Return circuits, vehicle harness and ECA.
  1. Checking System Integrity  - Visually check all wiring, harnesses, connectors and components for evidence of damage, overheating, shorting or looseness. If a fault is found, repair as necessary. If no faults are found, go to next step.
  2. Checking VAT Sensor Resistance  - Ensure key is off and install breakout box. Leave ECA disconnected. Set VOM on 100-ohm scale. Measure resistance between test pins No. 25 and 46. Compare resistance to VAT SENSOR RESISTANCE SPECIFICATIONS  table. If resistance is specification, go to next step. If resistance is not to specification, go to step 6).
    VAT SENSOR RESISTANCE SPECIFICATIONS

    Temperature °F (°C) Ohms
    -4° (-15°) 13,600-18,400
    68° (20°) 2210-2690
    140° (60°) 493-667
  3. Checking VAT Sensor Voltage  - With breakout box installed, set VOM on 10-volt scale. Turn key on and measure voltage between test pins No. 25 and 20. At 68°F (20°C), voltage should be 2.5 volts. Measure the voltage between test pins No. 46 and 20 (ground). At 68°F (20°C), voltage should be zero volts. Voltage will decrease if ambient temperature increases. If both voltages are as specified, there is an internal fault in the ECA, replace ECA. If voltage readings were not, as specified, go to next step.
  4. Checking For Short Between VAT & ECA  - Ensure key is off. Disconnect battery negative (-) cable. Install breakout box and leave ECA disconnected. Set VOM on 200-ohm scale. Measure resistance between the following test pins:
    • Test pins No. 25 and 26
    • Test pins No. 25 and 1
    • Test pins No. 25 and 37
    • Test pins No. 25 and 20 (ground)
    • Test pins No. 46 and 26
    • Test pins No. 46 and 1
    • Test pins No. 46 and 37

    If any resistance is less than 5 ohms, repair shorted circuit. If all circuits have a resistance of 5 ohms or more, go to next step.

  5. Checking Signal Return  - With key off, install breakout box and set VOM on 200-ohm scale. Measure resistance between test pins No. 46 and 20 (ground). If resistance is less than 5 ohms, replace ECA. If resistance is 5 ohms or more, go to CIRCUIT TEST A3  , step 1).
  6. Checking Open Circuits Between ECA & VAT  - With key off, install breakout box and leave ECA disconnected. Set VOM on 200-ohm scale. Measure resistance between test pin No. 25 and "R" wire at VAF sensor. Measure resistance between test pin No. 46 and "GN/Y" wire at VAF sensor. If both resistances are less than 5 ohms, go to next step. If either resistance is 5 ohms or more, repair open circuit as necessary.
  7. Checking VAT Sensor Resistance  - With key off, disconnect VAT sensor and set VOM on 10k-ohm scale. Ensure temperature is approximately 68°F (20°C). Measure resistance between sensor terminals "D" and "G". Measure resistance between sensor terminals "C" and "G". If both resistances are 2000 2700 ohms, repair short in "R" wire. If resistances are not as specified, replace VAF sensor.
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