Technical Description of OBD-II Trouble Code
The circuit for the Ambient Air Temperature Sensor is experiencing low 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, VW, and Volvo vehicles.
The Ambient Air Temperature (AAT) sensor converts the temperature of the surrounding air into an electrical signal for 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) inputs. When the ignition switch is first turned on after a long cool down period, the PCM compares the voltage from the AAT sensor to the readings from the IAT/ECT sensors. If there is too much variation, 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. Typically, this code is triggered by electrical problems.
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 P0072 trouble code may include:
Possible Solutions
It is always a good idea to check for technical service bulletins (TSB) specific to your vehicle. There may be a known issue with a known fix 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. Look for any signs of scraping, rubbing, bare wires, burn spots, or melted plastic. Disconnect the connectors and carefully examine the terminals inside. Check for any signs of burning or corrosion (indicated by a green tint). If necessary, clean the terminals using electrical contact cleaner and a plastic bristle brush. Allow them to dry and apply electrical grease to the contact points.
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 terminal on the sensor and the Black (Negative) lead to the other terminal. Determine the temperature outside (ambient air temperature) and refer to the resistance 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 P0072 code returns. If it does not, then the issue was most likely related to the connections.
If the P0072 code does reappear, 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 connected 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 display a value other than the ambient air temperature (which is typically a very low temperature) in degrees or 5 volts. Next, turn the ignition switch off, connect a jumper wire across the two terminals inside the harness connector for the AAT sensor, and then turn the ignition switch on. It should display a value close to 0 volts or something other than the ambient air temperature (which is typically a very high temperature) in degrees. If there is no 5 volts to the sensor or if there is no change in the readings, you will need to 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 P0072 code continues to appear, it is likely that the AAT sensor has failed. However, it is also possible that the control module has failed, so it cannot be ruled out until the AAT sensor is 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.
