P0073
PowertrainAmbient Air Temperature Sensor Circuit High
This is almost always a small, cheap job, so don't let it worry you. The ambient air temperature sensor sits out at the front of the car, and the ECU has seen the voltage on its circuit climb higher than it should. That usually points to a broken connection or a knackered sensor rather than anything expensive. The sensor that feeds your outside temperature display and helps the climate control is just reading wrong, or not reading at all.
ⓘ Information only. This page provides general educational information about fault code P0073. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0073 mean?
P0073 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Ambient Air Temperature Sensor Circuit High.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, sometimes with nothing else obvious going on
- • Outside temperature display showing something daft like -40C, or stuck at one figure all day
- • Automatic climate control behaving oddly or dropping back to manual
- • Cabin heating or air con not quite getting the temperature right
- • No reading at all where the outside temp normally sits
- • A small dip in economy here and there, easy to miss
Possible causes
Causes commonly associated with P0073, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Corroded or loose connector at the sensor, the most common cause by a mile given the sensor lives out in the weather at the front of the car
- 2. Break or open circuit in the wiring between the sensor and the ECU, often from chafing or a previous bumper repair
- 3. Failed sensor itself, they do eventually pack up after years of road spray and salt
- 4. Physical damage to the sensor from a stone, a low kerb knock, or a minor front-end shunt
- 5. Moisture sitting in the connector, which sends the voltage high until it dries out or gets cleaned
- 6. Short to a voltage supply on the signal wire, less common but it does happen
- 7. Internal fault in the control module, rare and last on the list for a reason
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull the sensor connector apart and look inside it. Green corrosion, water, or bent pins is your answer most of the time. Clean it, reseat it, and see if the fault clears
- 2. Find the sensor (front grille, behind the lower bumper, or near the radiator depending on the car) and check it hasn't taken a knock or had a stone through it
- 3. With the ignition on and engine off, check the signal voltage at the sensor. A reading pinned high tells you the circuit is open somewhere
- 4. Test continuity and resistance back to the ECU against the manual figures. This is where you find a broken wire the connector inspection missed
- 5. Clear the code, take it for a drive, and watch the live ambient temp data to confirm it now tracks the actual outside temperature
Common questions about P0073
Can I sort this myself in the driveway? +
Often, yes. Find the sensor at the front of the car, unplug it, and have a proper look in the connector. If it's full of green crud or damp, clean it with electrical contact cleaner, dry it, push it back together firmly, and clear the code. That fixes a fair number of these for the price of a can of cleaner. If the connector's clean and the fault stays, you're into checking the wiring with a multimeter, and a new sensor is usually a cheap part and a five-minute swap once you can reach it.
If I just clear the code, will it stay gone? +
Only if you've fixed what caused it. Wipe the code on a dodgy connector and the light will come straight back the next time the circuit reads high, sometimes within a few miles. If you cleaned the connector and the reading now follows the real outside temperature, you're sorted. If you've cleared it without touching anything, you're just resetting the clock on the same fault.
What happens if I leave it and keep driving? +
Mechanically, not much. The car will run fine and you can carry on driving it. The annoyances are a wrong or missing outside temp display and climate control that doesn't quite play ball. The real catch is the warning light. While it's on for this, it's masking anything more serious that might crop up, and if the light's lit when you take it for an MOT that can cause you a headache. It's a cheap fix, so there's little reason to live with it.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →