P0071
Ambient Air Temperature Sensor Range/PerformanceP0071 is a generic OBD-II powertrain diagnostic trouble code: Ambient Air Temperature Sensor Range/Performance. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0071 means
P0071 is set when the powertrain control module (PCM) determines that the signal from the Ambient Air Temperature (AAT) sensor is implausible — it does not rationally correlate with the Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) readings. The PCM performs a cross-check: if the AAT reading diverges from the other temperature sensors by more than approximately 10 °C (18 °F) under conditions where they should agree (e.g., a cold soak start), the sensor is declared irrational and the fault is stored.
The AAT sensor is a thermistor mounted in the front bumper or grille area, exposed to ambient air flow. Unlike the IAT sensor in the intake tract, it is subject to road debris, moisture, and connector vibration which can alter its resistance curve without producing an outright open or short — hence the rationality fault code rather than a circuit-level code. It primarily feeds the HVAC system's outside temperature display and can influence cold-start fueling trim and charge-air temperature models.
This code does not typically cause a drivability emergency. The PCM substitutes a default temperature value and continues normal operation. The MIL illuminates as a warning, and the outside temperature gauge may read incorrectly or freeze. HVAC automatic climate control may behave abnormally as a secondary effect.
Common causes
Most-frequently reported root causes when P0071 is logged.
-
1
Faulty or degraded AAT sensor with a shifted resistance curve that reads plausibly but disagrees with IAT/ECT cross-checks.
-
2
Corroded or moisture-contaminated AAT sensor connector causing intermittent resistance changes.
-
3
Sensor improperly mounted or displaced from its designed location, exposing it to heat soak from the radiator or engine bay.
-
4
Damaged wiring harness between the AAT sensor and the PCM (chafing, pinch points near the bumper).
-
5
IAT or ECT sensor out of calibration, causing a false rationality mismatch rather than a true AAT fault.
-
6
PCM software anomaly or intermittent internal reference voltage issue (rare).
Symptoms drivers notice
How to diagnose P0071
A typical diagnostic flow when this code is present.
-
1
Connect an OBD-II scanner and record freeze-frame data; note the AAT, IAT, and ECT readings at fault set time.
-
2
With ignition on and engine cold-soaked, compare live AAT sensor reading to actual ambient temperature — a large discrepancy confirms sensor or circuit fault.
-
3
Visually inspect the AAT sensor connector and harness at the front bumper/grille for corrosion, pushed-out pins, and chafing damage.
-
4
Measure the sensor resistance with a digital multimeter and compare to the manufacturer's temperature-resistance chart; replace the sensor if out of spec.
-
5
Check wiring continuity and insulation resistance from the sensor connector back to the PCM connector; repair any open or high-resistance segments.
-
6
Clear the code, perform a test drive through a range of temperatures, and verify no re-set.
-
7
If the code returns with correct sensor and wiring, inspect IAT and ECT sensors for accuracy before suspecting PCM.
Vehicles where we've handled P0071
Platforms in our catalogue with confirmed P0071 coverage.
Related powertrain codes
Frequently asked questions
Is it safe to drive with a P0071 code?
Yes, P0071 is generally a low-severity code. The engine runs on a default temperature value and drivability is rarely affected. However, the underlying fault should be diagnosed promptly because an inaccurate AAT reading can subtly affect cold-start fueling and climate control accuracy.
Will P0071 fail an emissions test?
In most jurisdictions, any stored fault code with the MIL illuminated will cause an OBD-II emissions failure. The code itself does not indicate an emissions-relevant failure, but the illuminated MIL is the disqualifying condition.
How is P0071 different from P0072 or P0073?
P0071 is a rationality (performance) fault — the sensor is electrically functional but its reading does not make sense compared to other temperature inputs. P0072 and P0073 are circuit-level faults where the sensor voltage is measurably below or above the valid operating range.
Can a bad IAT or ECT sensor cause a false P0071?
Yes. Because the PCM detects P0071 by comparing AAT against IAT and ECT, a drifted or failed IAT or ECT sensor can produce a false rationality mismatch. Always verify all three sensors are within spec before replacing the AAT sensor.
Disabling P0071 in software
RaceTune can permanently disable P0071 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P0071 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C50 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P0071 in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file