CTS 2003-2005

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 (100,000 ohms at -40°F.) while high temperature causes low resistance (70 ohms at 266°F.). The PCM supplies a voltage (about 5.0V) through a pull up resistor to the PCM's IAT signal circuit and measures the voltage. The voltage will be high when the in coming air is cold, and low when the air is hot. By measuring the voltage, the PCM calculates the in coming air temperature. The IAT sensor signal is used to adjust spark timing according to incoming air density.

A technician's scan tool displays the temperature of the air entering the engine, which should read close to the ambient air temperature when the engine is cold, and rise as the underhood temperature increases. If the engine has not been run for several hours (overnight), the IAT sensor temperature and engine coolant temperature displays should be close to each other. A failure in the IAT sensor circuit should set a Diagnostic Trouble Code.

Removal & Installation

Care must be taken when handling the IAT sensor. Damage to the IAT sensor will affect proper operation of the fuel injection system.

The IAT sensor is located on the air intake housing, near the Mass Air Flow (MAF) sensor.

Click image to see an enlarged view

Fig. The IAT sensor is located upstream in the air intake system and is usually close to the Mass Air Flow sensor-3.5L (VIN H) engine shown, other similar

  1. Detach the electrical connector.
  3. Carefully grasp the sensor and twisting counterclockwise, remove the IAT sensor from the air intake duct.
  5. Installation is the reverse of removal.


Check the following items before beginning more in depth diagnosis and testing.

Check for poor connection at the PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections.
Look for a damaged harness or damaged wiring going to the IAT sensor, especially if heavy work has recently been done where the connector could have been damaged.

Click image to see an enlarged view

Fig. IAT sensor resistance value chart

  1. Turn the ignition switch OFF .
  3. Disconnect the wiring harness from the IAT sensor.
  5. Measure the resistance between the sensor terminals.
  7. Compare the resistance reading with the accompanying chart.
  9. If the resistance is not within specification, the IAT may be faulty.
  11. Connect the wiring harness to the sensor.