P0071 – Ambient Air Temperature Sensor Range/Performance
The P0071 diagnostic trouble code indicates that the Engine Control Module (ECM) has detected that the Ambient Air Temperature (AAT) sensor signal is outside the expected operating range or does not match actual ambient conditions.
The ECM monitors the ambient air temperature sensor to support climate control operation and, on some vehicles, engine management strategies. If the sensor reading is implausible or changes abnormally, the ECM stores the P0071 code and illuminates the Check Engine Light.
Common Symptoms
- Check Engine Light ON
- Incorrect outside temperature display
- Poor automatic climate control performance
- Delayed or incorrect A/C operation on some vehicles
Common Causes
- Faulty ambient air temperature sensor
- Sensor contaminated by dirt or water
- Damaged or corroded wiring
- Loose electrical connector
- Sensor installed near a heat source
- Rarely, a faulty ECM
Basic Diagnosis
Compare the ambient temperature reading on a scan tool with the actual outside temperature. Inspect the sensor, wiring, and connector for damage or corrosion, verify the reference voltage and ground, and measure the sensor resistance according to the manufacturer's specifications.