Fault code P00A9 – intake air temperature circuit intermittent/erratic (Sensor 2, Bank 2)

Fault code P00A9 is called “Intake Air Temperature (IAT) Circuit Intermittent/Erratic (Sensor 2, Bank 2)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P00A9

This Diagnostic Trouble Code (DTC) is a generic code. Error P00A9 is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P00A9 – intake air temperature circuit intermittent/erratic (Sensor 2, Bank 2)

Forced induction from one engine cylinder is used to get more power from the cylinders. By forcing more air into the cylinder, more oxygen is produced during combustion. Therefore, the ECM (Engine Control Module) injects more fuel, resulting in more power.

Forced induction engines have two IAT (inlet air temperature) sensors whose resistance varies with temperature. As the temperature rises, the resistance decreases. A low temperature results in a high signal voltage.

Changes in the reference voltage are monitored by the PCM to calculate the air temperature. If the PCM detects a certain number of intermittent signals from IAT sensor 2 bank 2 within a specified period of time. The Check Engine light illuminates and the DTC P00A9 OBDII error code is stored.

Symptoms of vehicle malfunctions

The main signal that an error P00A9 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The Check Engine light on the control panel will illuminate (the code will be written to the ECM memory as a fault).
  2. The vehicle engine may be unstable under load or acceleration.
  3. The engine may run on too lean or too rich fuel mixture, depending on the outside temperature.
  4. But more often, no symptoms are felt.

Factors that can cause this error code

The error code P00A9 can mean that one or more of the following problems have occurred:

  • Internal malfunction of the IAT sensor No. 2.
  • Faulty connection on IAT No. 2 sensor.
  • Excessively high intake air temperature.
  • IAT sensor signal circuit may be shorted.
  • Sensor wiring is too close to high voltage wiring (e.g. alternator, spark plug cables, etc.).
  • Intake air temperature sensor wiring harness is broken or shorted.
  • Damaged connector or open circuit in engine control module (ECM).

The intake air temperature sensor (IAT) contains a semiconductor device that changes resistance in response to temperature (thermistor). It is located in the engine intake duct and has a signal and ground circuit. The transmission control module (PCM) monitors the sensor signal and sets the OBDII code P00A9. When the intake air temperature sensor signal is out of factory specification.

How to fix or reset OBD-2 code P00A9

Some suggested steps for troubleshooting and fix the error code P00A9:

  1. Check the IAT sensor wiring or connectors for a problem. You should repair or replace these components if they are in poor condition.
  2. Make sure the intake air temperature sensor is installed correctly and in the correct location. Make the appropriate adjustments.
  3. Use an error scanner to check the IAT sensor reading. If the engine is cold, the reading should match that of the coolant temperature sensor. If there is a difference in comparison, measure the resistance on the two leads of the IAT sensor. It must be replaced if it does not meet resistance requirements.
  4. Check for continuity between ground and IAT sensor signal cable.
  5. Check that 5 volt voltage is present. Repair if necessary.

Diagnose and repair of problems

Check with a scan tool to see if the IAT sensor can be read. If a reading can be taken and is within tolerance, the problem is most likely intermittent. If the reading is less than -22°F degrees, disconnect the connector.

Install a jumper between the wiring harness connector signal circuits and the ground circuits. The IAT temperature reading on the diagnostic tool should be as high as possible. For example, it should be 284 degrees Fahrenheit or higher. If so, there is nothing wrong with the wiring, there may be a connection problem.

If there is a problem getting data from the scan tool, it is likely that the sensor signal is missing due to a problem in the 5 volt line. Use a multimeter to check the signal continuity between the PCM connector and the IAT connector.

On which vehicles does this problem occur most frequently

Fault code P00A9 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Ford
  • Mazda
  • Mercedes-Benz

Fault code P00A9 can sometimes be found with other errors. The most common are the following: P00A5, P00A6, P00A7, P00A8.


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