GM Cadillac Deville_Fleetwood_ELD_Seville 1990-1998

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.  

REMOVAL & INSTALLATION



3.0L Engine
  1. Disconnect the wiring harness from the IAT sensor.
  2.  
  3. Remove the IAT sensor with the rubber grommet carefully from the air intake duct.
  4.  


NOTE
Excessive force may damage the sensor.

  1. Remove the rubber grommet from the IAT sensor.
  2.  

To install:

  1. Install the rubber grommet onto the IAT sensor.
  2.  

4.6L Engine
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the intake manifold cover.
  4.  
  5. Remove the Intake Air Temperature (IAT) sensor from the fuel rail.
  6.  

To install:

  1. Installation is the reverse of the removal procedure. Tighten the intake manifold cover bolts to 106 inch lbs. (12 Nm).
  2.  

4.9L Engine

The Intake Air Temperature sensor (IAT) is the same sensor as the Manifold Air Temperature (MAT) Sensor, the name has been changed. It operates in the same manner and performs the same function.


NOTE
When servicing the MAT sensor, be careful not to damage the tip of the sensor. Damage to the MAT sensor tip will affect proper operation of the fuel injection system.

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the electrical connector to the MAT sensor.
  4.  
  5. Unscrew the MAT sensor from the intake manifold.
  6.  

To install:

  1. Installation is the reverse order of the removal procedure. Prior to installing the sensor, coat threads with a nonhardening sealant.
  2.  



Click image to see an enlarged view

Fig. Intake Air Temperature (IAT) sensor-4.9L engine shown

 
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