P0071Ambient Air Temperature Sensor Circuit A Range/Performance
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- The ambient air temperature sensor A is an NTC thermistor whose resistance falls as temperature rises. Its value is used by the climate control, the outside temperature display and the engine control module, which needs it to enable other diagnostics and to correct its maps. Depending on the vehicle the engine control module reads the sensor directly, or the instrument cluster or another module sends the value over the data bus; some vehicles have no sensor and estimate ambient temperature from intake air temperature. P0071 is a plausibility check: after a long standstill (several hours) ambient, intake air and coolant temperatures should be close together. If the ambient reading deviates by more than a threshold at the next start, the code is set; an engine block heater or strong sunshine are excluded where the system can detect them.
- What you may notice
- Wrong or missing outside temperature display
- Climate control regulates incorrectly
- Check engine light on (manufacturer-dependent)
- Other monitors may not complete
- Likely causes
- LikelySensor drifting
- PossibleSensor mounted in a heat-affected spot, e.g. after a repair
- PossibleActually the comparison sensor (intake air or coolant) is faulty
- PossibleContact resistance at the connector
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €40 – €200
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.