Code
P0071
Generic
P — Powertrain
Ambient Air Temperature Sensor Circuit A Range/Performance
Views:
UK: 24
EN: 47
RU: 28
AI status
Completed
Completed
100%
Causes
- Faulty ambient air temperature (AAT) sensor / outside air temp sensor
- Open or short in sensor wiring (to power, ground or signal)
- Corroded, loose or damaged sensor connector/pins
- Sensor installed in incorrect location or blocked/affected by engine heat
- Intermittent wiring/connector fault (water intrusion, broken strand)
- PCM/ECM input circuit fault (rare)
Symptoms
- Exterior temperature gauge or dash display incorrect or erratic
- Climate control/automatic HVAC logic behaving improperly (incorrect blower/recirculation decisions)
- Stored P0071 fault code and possible MIL illumination depending on vehicle
- Intermittent or no change in reported ambient temperature when environmental temperature changes
What to check
- Retrieve freeze-frame and live data with a scan tool; note ambient air temp reading and compare to actual outside temp
- Visually inspect sensor location (usually front bumper, behind grille) and wiring/connector for damage, corrosion or contamination
- Backprobe sensor connector with key on and engine off to check reference voltage and signal voltage
- Measure sensor resistance at ambient and compare to expected resistance vs temperature chart for the vehicle (or compare to a known-good sensor)
- Check continuity/shorts between sensor and ECM connector (pin-to-pin) for open, short to ground, and short to battery voltage
- Wiggle test harness while monitoring live data for intermittent faults
Signal parameters
- Typical sensor type: NTC thermistor (resistance changes with temperature)
- Expected signal behavior: signal voltage or resistance should change smoothly as ambient temperature changes (no jumps)
- Common voltage range seen at the ECM/sensor: approx. 0.2–4.8 V depending on design (vehicle-specific)
- Typical resistance behavior: higher resistance at lower temps, lower resistance at higher temps (values vary by manufacturer)
- Fault conditions: open circuit → high or no voltage/sensor out-of-range; short to ground → very low voltage; short to battery → near constant high voltage
Diagnostic algorithm
- Confirm DTC and note freeze frame/conditions with a scan tool; clear code and see if it returns
- Compare the vehicle’s reported ambient temperature to a known accurate thermometer placed at the sensor location (allow time for equilibration)
- Turn ignition off, disconnect sensor, measure sensor resistance at current ambient temperature and compare to expected values (vehicle service data)
- With connector connected, backprobe to measure signal voltage with ignition on; verify reference voltage (if present) and ground are within specification
- Inspect wiring harness from sensor to ECM for damage; perform continuity test between sensor signal pin and ECM pin, and check for shorts to battery and ground
- Repair any damaged wiring or connector corrosion; if wiring is good and readings are out of specification, replace the ambient air temperature sensor
- After repair, clear codes, perform a road or ambient temperature change test and confirm code does not return
Likely causes
- Failed temperature sensor
- Damaged or shorted wiring between sensor and ECU
- Corroded or loose connector at sensor
Fault status
Status
Ambient Air Temperature Sensor Circuit A — Range/Performance (P0071)
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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