Ambient Air Temperature Sensor Range/Performance
The Powertrain Control Module (PCM) detected that the ambient air temperature (AAT) sensor signal is out of the expected range or not correlating with other temperature sensors after a cold soak. This indicates the sensor is providing an implausible reading based on current operating conditions.
This code does not typically affect the vehicle's drivability or safety. However, it can disable the air conditioning system and slightly impact fuel economy, so it should be addressed at your convenience.
Common symptoms
- Illuminated Check Engine Light
- Inaccurate outside temperature display on the dashboard
- Air conditioning system fails to cool or operates erratically
- Automatic climate control system does not regulate cabin temperature properly
- Slight decrease in fuel efficiency
Likely causes
- Faulty ambient air temperature (AAT) sensor
- Damaged, corroded, or loose wiring or connector at the AAT sensor
- Sensor blocked by debris or improperly mounted behind the grille
- Faulty Intake Air Temperature (IAT) or Engine Coolant Temperature (ECT) sensor causing a correlation mismatch
- Powertrain Control Module (PCM) software issue or failure
What to check before replacing parts
Visually inspect the ambient air temperature sensor and its wiring harness.
Look for: Look for physical damage, corrosion in the connector, or broken wires near the front bumper or grille area.
Compare the dashboard outside temperature display to the actual outside temperature.
Look for: A reading that is significantly off (e.g., showing -40 degrees on a warm day) indicates a sensor or circuit failure.
Use a scan tool to monitor AAT, IAT, and ECT sensor data after the vehicle has sat overnight (cold soak).
Look for: All three temperature readings should be within a few degrees of each other before starting the engine. A large variance in the AAT reading points to the sensor.
Disconnect the AAT sensor and test the circuit for proper reference voltage and ground.
Look for: You should typically see a 5-volt reference signal from the PCM and a good ground. If either is missing, there is a wiring or PCM issue.
Measure the resistance of the AAT sensor using a multimeter and compare it to a factory temperature-resistance chart.
Look for: If the resistance is out of specification for the current ambient temperature, the sensor is internally faulty and requires replacement.
This page explains the generic P0071 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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