Technical Description of OBD-II Trouble Code
The circuit for the Ambient Air Temperature Sensor is experiencing intermittent issues.
What does that mean?
This particular diagnostic trouble code is applicable to all vehicles equipped with OBDII.
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) 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 triggered. 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 caused by electrical problems.
The troubleshooting steps may differ depending on the manufacturer, type of AAT sensor, and wire colors.
Symptoms
The symptoms may include:
Causes
Possible causes of a P0074 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 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. 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. After cleaning, let them 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 post on the sensor and the Black (Negative) lead to the other post. Determine the temperature of the sensor (the outside temperature) and compare it to the resistance values 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), it means the sensor has failed.
If you have a scan tool, clear the diagnostic trouble codes from memory and see if this code reappears. If it doesn’t, then the issue was most likely due to the connections.
If the P0070 code does reappear, you will need to test the AAT sensor and its associated circuits. 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 (assuming the PCM is the module receiving the AAT sensor input). Read the AAT sensor temperature or voltage. It should display a value of 5 volts or something other than the ambient air temperature (which is a very low temperature) in degrees. 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 display a value close to 0 volts or something other than the ambient air temperature (which is a very high temperature) in degrees. If there is no 5 volts reaching the sensor or if you see no change, you will need to repair the wiring between the PCM and the sensor or consider the possibility of a faulty PCM.
Reconnect the sensor and wiggle the connector while monitoring the voltage or degrees from the AAT sensor. If you notice any changes while wiggling the wires, it indicates an intermittent connection. Take note of the wire routing and check for any points where the wires may be touching or rubbing against body panels or the frame.
If all previous tests have passed and you continue to encounter a P0070 code, 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.
