Technical Description of OBD-II Trouble Code
The circuit for the Ambient Air Temperature Sensor is registering a high voltage.
What does that mean?
This particular diagnostic trouble code is applicable to all engines equipped with OBDII, but it is more commonly found in certain Audi, BMW, Chrysler, Dodge, Ford, Jeep, Mazda, Mitsubishi, and VW vehicles.
The Ambient Air Temperature (AAT) sensor converts the temperature of the surrounding air into an electrical signal that is sent to the Powertrain Control Module (PCM). This information is used to adjust the operation of the air conditioning system and display the outside air temperature.
The PCM receives this input, along with the Intake Air Temperature (IAT) and Engine Coolant Temperature Sensor (ECT) readings, when the ignition switch is first turned on after a long cool down period. If there is too much variation between these inputs, this code is set. The PCM also checks the voltage signals from these sensors to ensure they are accurate when the engine is fully warmed up. This code is typically triggered by electrical issues.
The troubleshooting steps may vary depending on the manufacturer, type of AAT sensor, and wire colors.
Symptoms
The symptoms may include:
Causes
Possible causes of a P0073 trouble code may include:
Possible Solutions
It is always a good idea to check for any technical service bulletins (TSB) related to your specific vehicle. There may be a known issue with a known solution provided by the manufacturer, which can save you time and money during the diagnosis process.
Next, locate the AAT sensor in your vehicle. It is usually located in front of the radiator, behind the grille or front bumper area. Once you find it, visually inspect the connectors and wiring for any signs of damage such as scraping, rubbing, bare wires, burn spots, or melted plastic. Disconnect the connectors and carefully examine the terminals inside for any signs of burning or corrosion. If needed, clean the terminals with electrical contact cleaner and a plastic bristle brush. Once dry, apply electrical grease to ensure proper contact.
The most common cause of this issue is faulty connections, with a failed sensor being the second most common cause due to its exposure to harsh environmental conditions.
While checking the connections, you can test the sensor using a Digital Volt-Ohm Meter (DVOM). With the ignition switch off, disconnect the sensor and connect the Red (Positive) lead of the DVOM to one post on the sensor and the Black (Negative) lead to the other post. Determine the temperature outside and compare it to the resistance value on the chart. The DVOM should display the corresponding resistance in ohms. If it shows either 0 ohms or infinite resistance (usually indicated by the letters OL), the sensor has failed.
If you have a scan tool, clear the diagnostic trouble codes from memory and see if the P0073 code returns. If it does not, then the issue was most likely due to the connections.
If the P0073 code does return, further testing of the AAT sensor and its associated circuits is necessary. Typically, there are 2 wires connected to the AAT sensor. With the ignition switch off, disconnect the harness going to the AAT sensor. Turn the ignition switch on and use a scan tool to access PCM data. Read the AAT sensor temperature or voltage. It should read 5 volts or a value other than the ambient air temperature (which is very low). Next, turn the ignition switch off, connect a jumper wire across the two terminals inside the harness connector going to the AAT sensor, and then turn the ignition switch on. It should read close to 0 volts or a value other than the ambient air temperature (which is very high). If there is no 5 volts to the sensor or if there is no change in the readings, repair the wiring between the PCM and the sensor or consider the possibility of a faulty PCM.
If all previous tests have been passed and the P0073 code continues to appear, it is likely that the AAT sensor has failed. However, the possibility of a failed control module cannot be ruled out until the AAT sensor has been replaced. If you are unsure, it is recommended to seek assistance from a trained automotive diagnostician. Keep in mind that PCMs must be programmed or calibrated to the vehicle in order to be installed correctly.
