Fault code P009A is called “Intake Air Temperature (IAT)/Ambient Air Temperature (AAT) Correlation” 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 P009A
Code P009A indicates a discrepancy in the correlation signals between the intake air temperature sensor (IAT) and the ambient air temperature sensor (AAT). Correlation is necessary so that no obstruction will interfere with the vital air flow to the engine intake.
IAT sensors usually consist of a thermistor protruding from a plastic housing on a two-wire stand. The sensor is inserted into the air intake pipe or air filter housing.
When the intake air temperature rises, the resistance level in the IAT resistor decreases, causing the voltage to change. When the air is colder, the IAT resistor resistance increases. The PCM senses these voltage changes in the IAT sensor signal as changes in the intake air temperature.
The ambient air temperature sensor (AAT) acts in much the same way as the IAT sensor. The ambient air temperature sensor is usually located near the grille.
Code P009A will be stored, and the Malfunction Indicator Light (MIL) may illuminate if the PCM detects a large difference in sensor signals. These signals must differ by more than the maximum allowable amount within a certain period of time.
Symptoms of vehicle malfunctions
The main signal that an error P009A has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.
It can also be warning signs such as:
- The “Check engine” control lamp on the control panel will illuminate (the code will be stored as a fault).
- There may be no symptoms other than the stored fault code.
- Poor engine performance and power loss.
- Increased fuel consumption.
Fault P009A is considered serious, as it affects the safety and drivability of the vehicle. Ignoring the fault may result in costly repairs, it is recommended to eliminate the problem as soon as possible.
Factors that can cause this error code
The error code P009A can mean that one or more of the following problems have occurred:
- Faulty intake air temperature sensor (IAT).
- Faulty ambient air temperature sensor (AAT).
- Open or short-circuited circuits and sensor connectors.
- Sometimes the cause is a faulty PCM module.
How to fix or reset OBD-2 code P009A
Some suggested steps for troubleshooting and fix the error code P009A:
- Connect the OBD-II scanner to the vehicle’s diagnostic connector and read all stored data and error codes.
- Before proceeding with diagnosis code P009A, clear any other errors that may be present.
- Inspect the electrical wiring related to the intake air temperature (IAT) sensor for shorts, opens, and damage.
- If necessary, repair or replace any wires that are shorted, broken, damaged, or corroded.
- Inspect the sensor connector for looseness and corrosion.
- Test the IAT sensor; if it is defective, replace it.
- Repeat steps 3-6, only in relation to the ambient air temperature sensor (AAT).
- If the problem persists, check and reprogram or replace the control module (PCM) if necessary.
Diagnose and repair of problems
You can begin diagnosing fault P009A by visually inspecting the intake air temperature sensors as well as the ambient air temperature sensors. Inspect the connectors, as well as the wires to the sensors.
Look for loose connections and damaged wiring, anything that might suggest a faulty contact. If damage is found, repair, then clear the code and see if it returns.
Circuit testing
Using a diagnostic tool, monitor the data parameters from the intake air temperature sensors as well as the ambient air temperature. Disconnect the IAT sensor, the value on the diagnostic tool should drop to a very low value.
Then connect a jumper to the terminals, the diagnostic tool should show a very high temperature. If this is the case, the problem is with the sensor and not with the circuit or PCM module. Do the same with the AAT sensor.
Check the sensors
Disconnect the intake air temperature sensor connector. Then measure the resistance between the two sensor leads with a digital multimeter set to ohms.
Start the engine and look at the values, they should decrease smoothly as the engine warms up. Check the engine temperature gauge on the dashboard to make sure the engine has reached operating temperature.
If the engine temperature increases but the IAT resistance does not decrease, the sensor is defective and must be replaced. Repeat all the actions with the AAT sensor. After fixing the found faults, the problem with the fault P009A should be solved.
On which vehicles does this problem occur most frequently
Fault code P009A can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:
- BMW
- Ford
- Jeep
- Mazda
- Mercedes-Benz (SLK300)
Fault code P009A can sometimes be found with other errors. The most common are the following: P0095, P0096, P0097, P0098, P0099.
