GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Intake Air Temperature Sensor

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OPERATION



The Intake Air Temperature (IAT) sensor is a thermistor, which changes value based on the temperature of air entering the engine. Low temperature produces a high resistance (100,000 ohms{100K ohms} at -40°C/-40°F), while high temperature causes low resistance (70 ohms at 130°C/266°F). The PCM supplies a 5 volt signal to the sensor through a resistor in the PCM 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 PCM calculates the incoming air temperature.

The IAT sensor signal is used to adjust spark timing according to incoming air density. The scan tool displays temperature of the air entering the engine, which should read close to ambient air temperature when the engine is cold, and rise as underhood temperature increases. If the engine has not been run for several hours (overnight) the IAT sensor temperature and engine coolant temperature should read close to each other.

TESTING



  1. Access the IAT; if necessary, remove it from the vehicle.
  2.  
  3. Connect a digital ohmmeter to the terminals of the IAT.
  4.  
  5. On a cold engine, compare the resistance of the sensor to the temperature of the ambient air.
  6.  
  7. With the DVOM connected to the IAT sensor, and a thermometer at the sensor end, heat the sensor slightly, with a blow dryer or similar tool. Watch as the temperature goes up and the resistance goes down. Check the temperature against resistance on the chart.
  8.  
  9. Allow the sensor to cool, then repeat the test.
  10.  
  11. If the sensor does not meet specs, it should be replaced.
  12.  

See Figures 1, 2 and 3

Click image to see an enlarged view

Fig. Fig. 1: Disconnect the Intake Air Temperature sensor connector.



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Fig. Fig. 2: The resistance of the IAT reads high because the engine is cold.



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Fig. Fig. 3: Just the heat from a blow dryer can cause a drastic drop in resistance. This IAT sensor tests good.

REMOVAL AND INSTALLATION



Vehicles with a 3.1L engine employed a TBI unit and a Thermostatic Air Cleaner (Thermac) unit. This system heated the air before it was ingested by the engine. Inside the air cleaner is a temperature sensor that reacts to air intake temperature and controls the amount of vacuum going to the diaphragm motor that controls the damper door.

3.4L Engine

See Figure 4



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Fig. Fig. 4: IAT Location for a 3.4L engine The IAT sensor is mounted in the rear air intake duct.

  1. Disconnect the electrical connector.
  2.  
  3. Carefully remove the IAT sensor (snaps into place).
  4.  

To install:
  1. Installation is the reversal of the removal procedure.
  2.  

See Figure 5



Click image to see an enlarged view

Fig. Fig. 5: Typical location of IAT sensor in 3.8L Engines applications

  1. Remove the air intake cover and filter element, to access the IAT, if necessary.
  2.  
  3. Disconnect the electrical connector.
  4.  
  5. Remove the retaining clip from the IAT sensor, if equipped, and remove the sensor.
  6.  

To install:
  1. Installation is the reversal of the removal procedure.
  2.  

 
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