Ambient Air Temperature Sensor Circuit High
Diagnostic trouble code P0073 indicates that the Powertrain Control Module (PCM) has detected a high voltage condition in the ambient air temperature (AAT) sensor circuit. This typically means the sensor's signal voltage has exceeded the maximum expected threshold, often pointing to an open circuit or a disconnected sensor.
This code is generally not a safety hazard and will not strand you. However, it can affect the automatic climate control system and slightly impact engine performance, so it should be addressed when convenient.
Common symptoms
- Illuminated Check Engine Light
- Inaccurate outside temperature display on the dashboard
- Automatic climate control (A/C) system not functioning properly
- Slight decrease in fuel economy
- Minor drivability issues or hesitation in some vehicles
Likely causes
- Disconnected ambient air temperature sensor
- Damaged or broken wiring in the AAT sensor circuit (open circuit)
- Corroded or damaged electrical connector at the sensor
- Faulty ambient air temperature sensor
- Short to voltage in the AAT sensor wiring
- Faulty Powertrain Control Module (PCM) or climate control module (rare)
What to check before replacing parts
Visually inspect the ambient air temperature sensor and its connector.
Look for: Look for a disconnected plug, physical damage to the sensor (often located behind the front grille), or severe corrosion on the connector pins.
Inspect the wiring harness leading to the AAT sensor.
Look for: Check for broken, chafed, or chewed wires that would cause an open circuit or a short to voltage.
Use a scan tool to monitor the AAT sensor live data.
Look for: Observe the temperature reading. If it reads an extreme negative value (e.g., -40°F), it confirms an open circuit or a completely failed sensor.
Test the sensor's resistance using a digital multimeter.
Look for: Disconnect the sensor and measure its resistance across the terminals. Compare the reading to the manufacturer's temperature-to-resistance chart; an infinite reading (OL) indicates an internally open sensor.
Check the reference voltage and ground at the sensor connector.
Look for: With the key on and sensor disconnected, verify there is a 5-volt reference signal and a good ground. Missing voltage or ground indicates a wiring issue back to the PCM.
This page explains the generic P0073 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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