What does it mean?
Aside from controlling the engine, the engine control module (ECM) is in constant communication with other modules, such as those can control the anti-lock braking system, automatic transmission, and climate control system. With regards to climate control, the ECM needs to know when to activate the air-conditioning compressor, which command is received from the climate control module (CCM).
Similarly, the CCM needs to know coolant temperature, ambient air temperatures, and air-conditioning compressor function, which signals it gets from the ECM. On vehicles equipped with automatic climate control, one simply selects the desired cabin temperature, or temperatures, depending on how many zones the system is equipped to handle. The CCM simply handles the rest, including application of heat or air conditioning, blend door positions, vent door positions, fan speed, and others.
To illustrate, if the driver selects 72 °F in automatic, the CCM takes into account outside and inside temperatures and coolant temperature when calculating how much heating or cooling to apply. If it’s 45 °F outside and 50 °F inside, the CCM will apply a heat from the heater core, until the inside temperature reaches the desired 72 °F.
On the other hand, if it’s 85 °F outside, and 100 °F inside, because you just got in your car on a hot summer day, the CCM will command maximum air conditioning and fan speed to cool off the cabin. To make these calculations, the CCM counts on a number of signals, such as outside ambient air temperature, one or more inside air temperatures sensors, air-conditioning clutch operation, engine coolant temperature, and others.
If there is a problem with one of the signals, the CCM sets a diagnostic trouble code (DTC) in memory. Depending on system design, a CCM DTC may need to be read directly from the CCM or it may command a DTC to be stored in the ECM. In case the CCM or ECM detects a problem with the outside ambient air temperature sensor circuit, it will set DTC P0071 Ambient Air Temperature (AAT) Sensor Circuit.
Additionally, the AAT signal may be used to display the exterior temperature, perhaps in the instrument cluster or in the climate control head unit itself. Note: A Range/Performance related code will be set when either a sensor or other component does not perform within the range the PCM (Powertrain Control Module) expects to see, given the current engine load/speed, and information gathered from other sensors.
The possible causes of Range/Performance codes are likely to be defective sensors as easily as they are likely to be the result of wiring issues that affect the operation of the affected sensor or component, which means that with these codes, it is important to regard all sensors and components as part of the control circuit the code refers to.