P0073
Ambient Air Temperature Sensor Circuit High InputP0073 is a generic OBD-II powertrain diagnostic trouble code: Ambient Air Temperature Sensor Circuit High Input. 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 P0073 means
P0073 is stored when the PCM detects that the Ambient Air Temperature (AAT) sensor circuit voltage is higher than the maximum threshold of the sensor's valid operating range — typically above approximately 4.8–4.95 V. This voltage level maps to an impossibly cold temperature below the sensor's lower-limit (because the NTC thermistor presents maximum resistance, hence maximum voltage drop, at very low temperatures). In practice, a high-voltage fault means the circuit is effectively open: no current flows, the pull-up voltage appears unloaded at nearly 5 V, and the PCM logs a high-circuit fault.
Common electrical causes include a broken signal wire (open circuit), a disconnected sensor, or an open internal thermistor element. A short of the signal wire to the reference voltage supply (5 V line) can also produce a fixed high reading. Because the AAT sensor is located in the front bumper or grille area, physical damage from road impacts or poor routing is a realistic cause of an open harness condition.
Like P0072, this code illuminates the MIL and causes the outside temperature display to show an extreme value or a default. Engine drivability is generally unaffected since the PCM substitutes a default temperature. HVAC automatic climate functions may behave abnormally.
Common causes
Most-frequently reported root causes when P0073 is logged.
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1
Open circuit in the AAT sensor signal wire (broken wire, damaged connector terminal, or corroded pin-to-wire crimp).
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2
AAT sensor internal open circuit — the thermistor element has failed in the high-resistance direction.
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3
Disconnected sensor connector (physical damage from road debris, improper bumper re-installation after body work).
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4
Signal wire shorted to the 5 V reference supply line, holding the circuit at maximum voltage.
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5
Corroded connector terminals increasing resistance to the point the PCM reads the circuit as open.
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6
PCM-side wiring damage between the AAT signal pin and the internal pull-up resistor (rare).
Symptoms drivers notice
How to diagnose P0073
A typical diagnostic flow when this code is present.
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1
Retrieve the code with a scanner and note freeze-frame data; check whether the AAT live reading is pegged at an extreme value.
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2
Physically inspect the AAT sensor and its connector in the bumper/grille area for mechanical damage, disconnection, or missing protective grommets.
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3
With key on, engine off, measure voltage at the sensor signal pin — a reading near 5 V (at non-extreme ambient temperature) confirms an open or disconnected circuit.
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4
Reconnect and wiggle-test the harness near the bumper and firewall pass-through while monitoring live AAT data; an intermittent reading suggests a broken wire rather than a failed sensor.
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5
Disconnect the sensor and measure its resistance with a multimeter; compare to the manufacturer temperature-resistance table — an open circuit (infinite resistance) confirms internal sensor failure.
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6
Inspect the signal wire all the way to the PCM connector for opens, especially at harness clips and stress points near moving panels.
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7
Repair or replace as appropriate, clear the code, and confirm with a road test that the AAT reading tracks ambient temperature changes.
Vehicles where we've handled P0073
Platforms in our catalogue with confirmed P0073 coverage.
Related powertrain codes
Frequently asked questions
Why does a high-voltage fault indicate a cold reading rather than a hot reading?
The AAT sensor is a negative-temperature-coefficient (NTC) thermistor, meaning resistance rises as temperature falls. The PCM applies a pull-up voltage through a resistor; high sensor resistance (cold) produces high voltage. An open circuit presents infinite resistance, so the circuit reads maximum voltage — mapped to the coldest end of the scale.
Could recent bumper or bodywork repairs cause P0073?
Yes. The AAT sensor connector is often disturbed during front bumper removal. If the connector was not fully seated after reassembly, or if the wiring was pinched in a panel gap, P0073 is a likely result. Always check the physical connection first.
Is P0073 dangerous to ignore?
Not immediately. The engine runs on a default temperature value and primary drivability is unaffected. However, the underlying open circuit means the HVAC system lacks accurate ambient data, and the fault should be repaired to restore correct climate control operation and clear the MIL.
How do I distinguish P0073 (open/high) from P0071 (rationality) if both can show an odd temperature?
P0073 will show a voltage at or very close to the reference supply (typically ~4.9–5 V), placing the reading at the extreme cold limit. P0071 shows a voltage within the valid range, but the reading disagrees with IAT and ECT. Checking the live sensor voltage on a scan tool distinguishes them clearly.
Disabling P0073 in software
RaceTune can permanently disable P0073 — 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 P0073 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.
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