P0099 OBD-II Trouble Code: Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic

Check Engine Light

P0099 code definition

Intake Air Temperature Sensor 2 Circuit Intermittent/Erratic

What the P0099 code means

P0099 is the OBD-II generic code that indicates that the engine control module (ECM) has detected a fault in the intake air temperature sensor 2 (IAT2). This code indicates that it is not operating in the normal sensor range and that the IAT2 has intermittent or erratic sensor input to the ECM.

What causes the P0099 code?

  • The erratic or intermittent IAT input causes the ECM to not trust the input reading and substitutes its input to 70° F.

  • The intake air temperature sensor 2 is not accurate within 2 degrees when compared to the engine coolant and the mass air temperature sensors when the engine is cold started after the engine has been off for more than 5 hours.

  • The intake air temperature sensor 2 is not within specification range within 2 degrees of the sensor when compared to the mass air flow sensor when started warm and heat soaked from 10 seconds to 30 minutes.

What are the symptoms of the P0099 code?

  • The Check Engine Light comes on to alert of a problem with the system.
  • The engine may run rough, hesitate, or surge while driving depending on ambient temperature difference from 70° F.

How does a mechanic diagnose the P0099 code?

  • Visually checks the electrical connections and wire harness to the intake air temperature sensor.

  • Scans and documents engine codes and checks freeze frame data for when the sensor failed.

  • Scans the IAT2 sensor and compares the output to be within specifications for when it fails in the freeze frame data to try and duplicate the sensor failure. They will lightly tap the sensor to see if the reading is erratic.

  • Disconnects the IAT2 sensor connector and verifies that the temperature reading goes below -4° F.

  • Shorts the two connector wires together to see if temperature readings go above 212° F.

  • While the connectors are shorted, they will do a wiggle test to see if any issues are found with the wiring or connections.

  • Using a multimeter to check that the ohms of the IAT2 sensor is within specifications while lightly tapping on sensor to see if the reading is erratic indicating a sensor internal failure.

  • Replaces the sensor if the sensor fails the wiggle test or is not within specifications.

Common mistakes when diagnosing the P0099 code

  • Not verifying failures by clearing the codes and testing to see if the problem returns
  • Not verifying freeze frame readings and wiggle testing the sensor for the failure
  • Replacing parts before conducting pinpoint tests and visual checks

How serious is the P0099 code?

  • The ECM will substitute a 70° F sensor input for the out of specification reading for the sensor.

  • The engine may run rough or hesitate if outside temperature is more than 10° F different from the 70° F the ECM uses as a substitute output.

  • The engine can hesitate and have a lack of power during acceleration depending on how different the outside temperature is from the default 70° F.

  • The engine will fail emission testing due to the Check Engine Light being on and the monitors not completed.

What repairs can fix the P0099 code?

  • Replacing the IAT2 sensor if it fails testing
  • Repairing or replacing the wiring or connection to the IAT2 sensor
  • Repairing the ECM connector or replacing the ECM

Additional comments for consideration regarding the P0099 code

The IAT2 code P0099 can be caused from corrosion in the connector that is causing the connection to go in and out but stays in specification when it does work. Sometimes a sensor has loose connections internally that can be duplicated during testing and lightly tapping on the sensor.

Need help with a P0099 code?

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