P0073 is an OBD-II trouble code that points to a problem with your vehicle’s ambient air temperature sensor circuit. In simple terms, your car’s computer is seeing a signal that’s higher than it should be from the outside temperature sensor. While this usually won’t leave you stranded, it can affect how your climate control works and, on some vehicles, even how the engine and transmission behave. In this guide, you’ll learn what P0073 means, common causes, symptoms, how to diagnose it, and what it typically costs to fix.
What Does P0073 Mean?
P0073 stands for “Ambient Air Temperature (AAT) Sensor Circuit High.” The ambient air temperature sensor measures the outside air temperature and sends that information to the ECU or body control module. A “circuit high” fault means the computer is seeing a voltage that’s higher than the expected range for that sensor.
This usually indicates an open circuit, damaged wiring, corrosion at the connector, or a failed sensor. On many cars, the same sensor feeds both the HVAC system and the engine management system, so a bad reading can affect more than just the temperature display on your dash.
Quick Reference
- Code: P0073 – Ambient Air Temperature Sensor Circuit High
- Severity: Low to moderate (comfort and efficiency issue, not usually a no-start)
- Common Causes: Bad AAT sensor, open wiring, corroded connector, previous front-end damage
- Typical Symptoms: Wrong outside temp reading, HVAC issues, possible fuel economy changes
- Typical Fix: Repair wiring or replace ambient temperature sensor, clear codes
Real-World Example / Field Notes
In the shop, I see P0073 most often after a front-end impact or minor collision repair. The ambient air temp sensor is usually mounted behind the front bumper or grille, and it’s easy to overlook when replacing a bumper cover. I’ve also seen plenty of cases where a car wash or road debris rips the sensor harness loose. The customer complains that the outside temperature reads 140°F on a cool morning, the A/C doesn’t cool properly at idle, and the check engine light is on. A quick inspection usually reveals a broken sensor or a connector hanging by a thread.
Symptoms of P0073
- Incorrect outside temperature display on the dash or infotainment screen (often stuck very high or reading “–”).
- HVAC performance issues, such as A/C not cooling well or automatic climate control blowing the wrong temperature.
- Check engine light (MIL) illuminated, sometimes along with a separate climate control warning.
- Poor fuel economy on some vehicles if the ECU uses ambient temperature for fuel and fan strategies.
- Erratic fan operation, with cooling fans running more than usual or at odd times.
Common Causes of P0073
Most Common Causes
- Failed ambient air temperature sensor – Internal open circuit or high resistance causes the ECU to see a high voltage signal.
- Unplugged or loose sensor connector – Often after bumper replacement, body work, or DIY repairs near the grille.
- Broken or chafed wiring – The harness runs low and forward; road debris, ice, or corrosion can break the wires.
- Corroded terminals – Water, salt, and dirt get into the connector and cause poor contact or open circuits.
Less Common Causes
- Incorrect sensor installed – Aftermarket or wrong-part sensor with improper resistance range.
- Previous collision damage – Hidden harness damage behind the bumper reinforcement or radiator support.
- Wiring issues inside the harness – Internal breaks or shorts between the sensor and ECU or body control module.
- Faulty ECU/BCM input – Rare, but a bad input circuit can falsely interpret a normal signal as “high.”
- Connector pin fit issues – Spread terminals that no longer grip the sensor pins tightly.
Diagnosis: Step-by-Step Guide
You’ll want a basic scan tool (preferably one that can read live data), a digital multimeter, and simple hand tools. Access to a wiring diagram for your specific vehicle is very helpful. If you’re comfortable with basic electrical checks, you can do most of this at home.
- Confirm the code. Connect a scan tool, read stored and pending codes, and verify P0073 is present. Check for related temperature or HVAC codes that might point to a bigger issue.
- Check the outside temperature display. Compare the dash reading to an accurate thermometer. If the display is way off (for example, 140°F when it’s 60°F), that supports an AAT sensor issue.
- Perform a visual inspection. Locate the ambient air temperature sensor, usually behind the front grille or bumper. Look for a broken sensor, missing sensor, damaged wiring, or a connector that’s unplugged or hanging loose.
- Inspect the connector closely. With the ignition off, unplug the sensor. Check for corrosion, bent pins, moisture, or spread terminals. Clean with electrical contact cleaner if needed.
- Check sensor resistance. With the sensor unplugged, use a multimeter to measure resistance across the two sensor pins. Compare the reading to a temperature vs. resistance chart (often NTC thermistor type). A reading of “OL” (open) or zero ohms usually indicates a bad sensor.
- Check for reference voltage and ground. Turn the key on (engine off). With the sensor unplugged, back-probe the harness connector. Most systems will show a 5V reference on one wire and a ground or signal return on the other. If you see battery voltage or nothing at all, check the wiring back to the ECU/BCM.
- Wiggle test the harness. While watching ambient temperature live data on the scan tool, gently move the harness and connector. If the reading jumps around or drops out, you likely have an intermittent wiring or connector issue.
- Check continuity to the ECU/BCM. If power and ground look good at the connector but the code persists, use the wiring diagram to check continuity from the sensor connector to the ECU/BCM pins. Repair any open or high-resistance circuits.
- Clear codes and retest. After repairs or sensor replacement, clear the codes, drive the vehicle, and monitor ambient temperature data and pending codes to confirm the fix.
Pro tip: On some vehicles, the ambient temperature reading updates slowly to avoid rapid swings. After replacing the sensor, you may need to drive for several minutes or cycle the ignition before the dash display and ECU data reflect the new, accurate reading.
Possible Fixes & Repair Costs
Most P0073 repairs are straightforward. Once you pinpoint the cause, you’re typically looking at one of the following fixes:
- Replace the ambient air temperature sensor.
- Repair or replace damaged wiring near the sensor.
- Clean or replace a corroded connector and terminals.
- Secure a loose harness after body or collision repairs.
- In rare cases, repair wiring deeper in the harness or address a faulty ECU/BCM input.
Typical repair costs for P0073 range from about $75–$250 at a shop. A simple sensor replacement usually runs $20–$80 for the part plus 0.5–1.0 hour of labor. Wiring repairs can add time and cost depending on how hard the harness is to access. If the issue traces back to collision damage or an internal module fault, costs can climb into the $300–$600+ range. Labor rates, vehicle make, and parts availability all affect the final bill.
Can I Still Drive With P0073?
In most cases, you can continue driving with P0073 without immediate risk of engine damage. The code primarily affects comfort and system accuracy rather than basic drivability. However, you may notice poor A/C performance, incorrect outside temperature readings, and slightly altered fuel economy or fan operation on some models. If you’re in extreme hot or cold weather, a malfunctioning ambient temperature input can make the HVAC system less effective, which can be uncomfortable and potentially unsafe in severe conditions. It’s best to address the issue soon rather than ignore it.
What Happens If You Ignore P0073?
If you ignore P0073, you’ll likely live with inaccurate outside temperature readings and subpar HVAC performance. Over time, the ECU may adjust fuel and cooling strategies based on incorrect data, which can slightly impact fuel economy and engine warm-up behavior. You also risk missing other new check engine codes because you’re used to seeing the light on. Fixing P0073 early keeps your climate control and diagnostics working the way they should.
Need wiring diagrams and factory-style repair steps?
Powertrain faults often require exact wiring diagrams, connector pinouts, and guided test steps. A repair manual can help you confirm the cause before replacing parts.
Related Sensor Ambient Codes
Compare nearby sensor ambient trouble codes with similar definitions, fault patterns, and diagnostic paths.
- P0098 – Intake Air Temperature Sensor 2 Circuit High
- P0074 – Ambient Air Temperature Sensor Circuit Intermittent
- P0072 – Ambient Air Temperature Sensor Circuit Low
- P0070 – Ambient Air Temperature Sensor Circuit
- P0538 – A/C Evaporator Temperature Sensor Circuit High
- P0517 – Battery Temperature Sensor Circuit High
Key Takeaways
- P0073 means the ECU sees a “high” signal from the ambient air temperature sensor circuit, usually from an open circuit or failed sensor.
- Common symptoms include wrong outside temperature readings, HVAC issues, and a check engine light, but little to no drivability change.
- Most causes are simple: bad sensor, damaged wiring, or a loose/corroded connector, often after front-end work or minor collisions.
- Diagnosis involves visual inspection, checking sensor resistance, verifying power/ground, and confirming wiring continuity.
- Repairs are typically affordable, with most fixes falling in the $75–$250 range depending on parts and labor.
Vehicles Commonly Affected by P0073
P0073 shows up across many brands because nearly all modern vehicles use an ambient air temperature sensor. In the shop, I commonly see this code on:
- GM vehicles – Chevrolet Silverado, Equinox, Malibu, GMC Sierra, Buick and Cadillac models.
- Ford and Lincoln – F-150, Escape, Explorer, Fusion, and related SUVs.
- Chrysler, Dodge, Jeep, Ram – Especially trucks and SUVs with exposed front-end sensors.
- Toyota and Lexus – Camry, Corolla, RAV4, Tacoma, and various Lexus crossovers.
- Honda and Acura – Civic, Accord, CR-V, and MDX/RDX models.
- Hyundai and Kia – Elantra, Sonata, Santa Fe, Sportage, and similar models.
It’s especially common on vehicles that see harsh winters, lots of road salt, or frequent front-end repairs, because the sensor and wiring are exposed to the elements.
FAQ
Can I clear P0073 myself and see if it comes back?
Yes, you can clear P0073 with a basic OBD-II scanner. If the issue is intermittent, the code may stay away for a while, but if there’s a real wiring or sensor fault, it will usually return after a few drive cycles. Clearing the code without at least inspecting the sensor and wiring isn’t recommended.
Is P0073 related to my A/C not getting cold?
It can be. Many automatic climate control systems use the ambient temperature reading to decide how hard to run the A/C. If the car thinks it’s much cooler or hotter outside than it really is, the system may not cool properly or may behave strangely. Fixing P0073 often restores normal A/C performance.
Where is the ambient air temperature sensor located?
On most vehicles, the ambient air temperature sensor is mounted at the front of the car, behind the grille or in the lower bumper area. It’s usually a small, two-wire sensor clipped to a bracket or the radiator support. Check your owner’s manual or a repair manual for the exact location on your model.
Can a bad ambient temperature sensor affect fuel economy?
On some vehicles, yes. The ECU may use ambient temperature to adjust warm-up strategies, fan operation, and sometimes fuel trims. A sensor stuck reading very hot or very cold can slightly impact fuel economy and drivability, especially during cold starts or extreme weather.
How do I know if it’s the sensor or the wiring causing P0073?
The best way is to test both. Measure the sensor’s resistance and compare it to a temperature chart; if it’s open or way out of range, the sensor is likely bad. If the sensor tests good, check for proper reference voltage and ground at the connector and verify continuity back to the ECU or body module. Any open circuit or damaged wiring points to a harness or connector issue rather than the sensor itself.