The diagnostic trouble code (DTC) P0073 in Ford vehicles indicates a problem with the Ambient Air Temperature (AAT) sensor circuit. This sensor plays a crucial role in the vehicle’s climate control system, providing the Powertrain Control Module (PCM) with information about the outside air temperature. This data is used to regulate the air conditioning (A/C) system and other climate-related functions. A high signal in the AAT sensor circuit can lead to various A/C issues, including the inability of the compressor to engage.
A 2014 Ford Fusion with 78,950 miles was brought in with the complaint of hot air blowing from all A/C vents. The refrigerant level was confirmed to be at the correct specification (20 oz). Attempts to command the A/C compressor “ON” with a scan tool failed. A scan revealed DTC P0073 – Ambient Air Temperature (AAT) sensor circuit high.
Following the Ford diagnostic Pinpoint Test “FA” in ALLDATA, the technician determined the AAT sensor was faulty, reporting -40°F. The sensor was replaced, and the DTC was cleared. However, the A/C compressor still wouldn’t engage, even though no DTCs were present. Applying power directly to the compressor resulted in normal A/C operation.
ALLDATA Tech-Assist was consulted. They recommended reviewing A/C-related temperature and pressure sensor readings via the scan tool to ensure accuracy and correlation. They also suggested checking if the PCM was denying A/C requests.
The technician inspected the sensors and found the A/C pressure transducer reporting only 4 psi under all conditions. Wiring diagrams were used to verify circuit integrity and rule out a PCM fault. Ultimately, the A/C pressure transducer was replaced, and the DTC was cleared. This resolved the issue, restoring proper A/C function with no recurring DTCs. The inaccurate pressure reading likely prevented the A/C system from engaging, demonstrating the importance of accurate sensor data for proper system operation. Although the initial diagnosis pointed to the AAT sensor, the root cause was ultimately the faulty A/C pressure transducer. This highlights the importance of thorough diagnostics and consulting resources like ALLDATA Tech-Assist when troubleshooting complex automotive issues.
