Description And Operation - Ambient Air Temp Sensor
The AAT Sensor is typically located in the front of the vehicle near the grill. On some vehicles the AAT Sensor is located in the drivers side mirror housing. The sensor is normally hard-wired to the Body Control Module (BCM) or Totally Integrated Power Module (TIPM) depending on vehicle architecture. On vehicles that have the sensor mounted in the mirror, it may be hard-wired to the Drivers Door Module (DDM), if equipped. Refer to the wiring information for the specific vehicle being diagnosed to determine which module to test at. The analog AAT Sensor signal is converted to a digital signal and broadcast over the vehicle Bus. If hard-wired to the DDM, it is bussed to the BCM/TIPM. The BCM/TIPM broadcasts the AAT Sensor signal over the Can C Bus. The Powertrain Control Module (PCM) acquires the AAT Sensor signal from the Can C Bus.
While circuit high and low faults are monitored by both the PCM and BCM, only the PCM performs a rationality diagnostic of the AAT Sensor signal.
The AAT Sensor rationality diagnostic runs on a cold start after a cold soak condition was present on the previous key off cycle. Following a start to run delay time, the PCM typically compares the signals from the AAT, Engine Coolant Temperature (ECT), and Intake Air Temperature (IAT) Sensors. If the ECT and IAT Sensors agree and the AAT Sensor does not agree, the AAT Sensor signal is declared as irrational. If declared irrational a second comparison will be done after a short drive cycle.
If a repair is performed to the AAT Sensor wiring, the sensor is replaced, or the BCM connector is disconnected during testing to correct an active DTC, the vehicle must be driven for a minimum of 5 minutes above 15 mph to update the AAT temp signal before the DTC will go stored and can be erased.