GM Astro/Safari 1985-1996 Repair Guide

Intake Air Temperature (IAT) Sensor

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OPERATION



See Figure 1



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Fig. Fig. 1: Typical intake air temperature sensor

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 ECM supplies a 5 volt signal to the sensor through a resistor in the ECM 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 ECM calculates the incoming air temperature.

The IAT sensor signal is used to adjust spark timing according to incoming air density.

TESTING



See Figure 2



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Fig. Fig. 2: Intake air temperature sensor resistance chart

  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.  

REMOVAL & INSTALLATION



See Figures 3, 4 and 5



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Fig. Fig. 3: The intake air temperature sensor pushes into the intake duct on the CMFI engines



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Fig. Fig. 4: The intake air temperature sensor screws into the intake manifold on the 4-cylinder engine



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Fig. Fig. 5: Intake air temperature sensor location on 1996 CSFI engine

  1. Disconnect the negative battery cable.
  2.  
  3. Disengage 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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