GM S-Series Pick-ups and SUV's 1994-1999 Repair Guide

Intake Air Temperature (IAT) Sensor

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OPERATION



The Intake Air Temperature (IAT) sensor is a thermistor which changes value based on the temperature of the air entering the engine. Low temperature produces a high resistance, while a high temperature causes a low resistance. The VCM supplies a 5 volt signal to the sensor through a resistor in the VCM and measures the voltage. The voltage will be high when the incoming air is cold, and low when the air is hot. By measuring the voltage, the VCM calculates the incoming air temperature. the IAT sensor signal is used to adjust spark timing according to incoming air density.

TESTING



See Figures 1, 2 and 3

  1. Remove the Intake Air Temperature (IAT) sensor.
  2.  
  3. Connect a digital ohmmeter to the two terminals of the sensor.
  4.  
  5. Using a calibrated thermometer, compare the resistance of the sensor to the temperature of the ambient air. Refer to the temperature vs. resistance illustration.
  6.  
  7. Repeat the test at two other temperature points, heating or cooling the air as necessary with a hair dryer or other suitable tool.
  8.  
  9. If the sensor does not meet specification, it must be replaced.
  10.  



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Fig. Fig. 1: Measuring the Intake Air Temperature (IAT) sensor resistance



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Fig. Fig. 2: Common Intake Air Temperature (IAT) sensor wiring diagram (wire color, terminal identification/location may vary on certain models)



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Fig. Fig. 3: Intake Air Temperature (IAT) sensor temperature vs. resistance values

REMOVAL & INSTALLATION



See Figures 4 and 5



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Fig. Fig. 4: Intake Air Temperature (IAT) sensor location

  1. Disconnect the negative battery cable.
  2.  
  3. Unplug the sensor electrical connection.
  4.  
  5. Loosen and remove the IAT sensor.
  6.  
  7. Installation is the reverse of removal.
  8.  



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Fig. Fig. 5: Use a twisting and pulling motion to remove the Intake Air Temperature (IAT) sensor

 
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