75 IAT Unstable

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Description

The air temperature sensor (ATS) is a thermistor located in the air intake passage of the air induction system on the engine. When the sensor is cold it has a high resistance, the resistance decreases as the temperature of the sensor increases. The PCM supplies a five volt signal to the sensor which is also connected to ground. The PCM reads the voltage drop on the sensor signal line to determine air temperature.

Information Flag Parameters

Information Flag 75 will set if:

  • ATS reading changes more than 15°C (59°F) in 100 milliseconds.

Diagnostic Aids

  • When attempting to diagnose an intermittent problem, use the Scan Tool to review supplemental diagnostic information. The supplemental data can be used to duplicate a problem. Select MALF History from Scan Tool EC menu.
  • Check the tightness of the female terminal grip with a spare male terminal.
  • Wiggle the ATS connector. Watch Scan Tool to see if ATS reading changes falls sharply.
  • Check ATS connector. Check for shorted terminals.
  • Wiggle and tug the harness. Watch Scan Tool to see if ATS reading rises or drops sharply.
  • Wiggle and tug the harness at the PCM. Lightly tap the PCM. Watch for changes in the ATS reading.
  • Check the PCM connector. Check for shorted terminals.

NOTICE: Information flags should be used for diagnostic purposes only. They do not necessarily indicate component malfunction/failure.