P0071: Ambient Air Temperature Sensor Circuit A Range/Performance

What does P0071 mean?

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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

• Wrong or missing outside temperature display
• Climate control regulates incorrectly
• Check engine light on (manufacturer-dependent)
• Other monitors may not complete

Common causes

• High Sensor drifting
• Medium Sensor mounted in a heat-affected spot, e.g. after a repair
• Medium Actually the comparison sensor (intake air or coolant) is faulty
• Medium Contact resistance at the connector

Likelihood is a general estimate across vehicles; your make and model may differ.