OBD-II Code P0073: Ambient Air Temperature Sensor Circuit High

What Does P0073 Mean?

P0073 means the Powertrain Control Module (PCM) detects a voltage signal from the Ambient Air Temperature (AAT) sensor exceeding the 4.9-volt maximum threshold. The PCM interprets this high voltage as an open circuit—typically a broken wire or unplugged sensor. As a failsafe, the computer ignores the invalid signal and defaults to a pre-programmed temperature of -40°F (-40°C).

Technical definition: The official SAE/ISO definition for P0073 is "Ambient Air Temperature Sensor Circuit High Input." This indicates the Powertrain Control Module (PCM) detects AAT sensor voltage above the calibrated threshold (typically >4.9V) for a set duration. This confirms an open signal circuit, an open ground circuit, or a short to voltage.

Can I Drive With P0073?

Yes, But With Caution. Yes, but fix it within a few weeks. While it doesn't impact core engine safety, it disables automatic climate control and defrosters. The incorrect temperature reading also forces the engine to run slightly rich. Over hundreds of miles, this stresses the catalytic converter, risking an $800-$2500 failure and unexpectedly disabling the auto start/stop system.

Common Causes

• Damaged Wiring or Corroded Connector (Very Common) — The AAT sensor's exposed location behind the grille or in a side mirror makes its wiring highly vulnerable to road debris, moisture, road salt, and rodents. Broken, frayed, or corroded wires are the number one cause of this open circuit fault.
• Unplugged Sensor / Post-Repair Oversight (Common) — Following front-end collision repairs, grille replacement, or bumper removal, technicians frequently forget to plug the AAT sensor back in. This leaves the circuit open, immediately triggering P0073 on the next startup.
• Missing Sensor from Aftermarket Mirror Swap (Common) — On many Ford, Dodge, and Ram trucks, the AAT sensor lives inside a side mirror. Replacing the factory mirror with a cheaper aftermarket tow mirror that lacks a built-in sensor guarantees this code.
• Failed Ambient Air Temperature (AAT) Sensor (Common) — The sensor is a thermistor that fails internally from age, vibration, or moisture intrusion. An internal break creates an open circuit, preventing it from pulling the reference voltage down and causing the PCM to read maximum voltage.
• Blown Fuse (Rare) — In some vehicles, the AAT sensor circuit is protected by a fuse. For example, on 2013-2018 Dodge Ram trucks, fuse F99 in the main fuse box links to temperature sensor circuits. A blown fuse creates an open circuit condition.
• Faulty Control Module (PCM, BCM, or TIPM) (Very Rare) — The vehicle's Powertrain Control Module (PCM) or Body Control Module (BCM) can suffer an internal fault. Consider this only after exhaustively testing the sensor, wiring, and connectors.

Symptoms

• Incorrect Outside Temperature Display — The dashboard or infotainment screen displays a stuck, default low value, almost always -40°F (-40°C).
• Automatic Climate Control Disabled — The A/C compressor fails to engage, or the automatic climate control blows warm air because the system believes it is freezing outside.
• Check Engine Light is On — The Malfunction Indicator Lamp (MIL) illuminates on the dashboard.
• Disrupted Auto Start/Stop Function — Modern auto start/stop systems rely on the AAT reading for operational logic. An invalid temperature reading disables the feature.
• Slight Decrease in Fuel Economy — Because the computer sees a -40°F reading, it enriches the fuel mixture, leading to a 5-10% decrease in gas mileage and occasionally a rough idle.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Reconnect Unplugged Sensor / Install Missing Mirror Sensor — Parts: $0-$40, Labor: $0-$75, ~0.5 hr book time (DIY)
• Clean Corroded Electrical Connector — Parts: $5-$15, Labor: $0, ~0.2 hr book time (DIY)
• Replace the Ambient Air Temperature Sensor — Parts: $15-$75, Labor: $50-$150, ~0.8 hr book time (DIY)
• Repair Damaged Wiring or Connector — Parts: $5-$40, Labor: $100-$200, ~1.5 hr book time (Intermediate)
• Replace Powertrain Control Module (PCM) — Parts: $700-$1000, Labor: $150-$200, ~1.2 hr book time (Professional)

DIY vs Professional

• Replace the Ambient Air Temperature Sensor — Beginner:
  Tools: Basic hand tools, trim removal tools.
• Clean Corroded Electrical Connector — Beginner:
  Tools: Electrical contact cleaner, small brush, dielectric grease.
• Repair Damaged Wiring or Connector — Beginner:
  Tools: Multimeter, wire strippers, heat-shrink butt connectors, heat gun.
• Replace Powertrain Control Module (PCM) — Beginner:
  Tools: Advanced diagnostic scan tool, socket set.

Used vs. New Parts: Buying Guide

When a used part is worth it: Buy new for a simple AAT sensor ($15-$75). Buying used only makes sense if the sensor is integrated into an expensive assembly like a complete side-view mirror ($300+ new) and you find a guaranteed-functional unit from a reputable recycler.

Donor-vehicle mileage cap: roughly under 60000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the used part comes with a 30-90 day warranty.
• For mirror assemblies, ensure all functions (power adjust, heat, signals) are tested.
• Avoid parts from rust-belt states, as corrosion kills these sensors.

Decision logic:

• If The part is just the sensor itself → Buy new. The cost saving for a used sensor is negligible.
• If The sensor is part of a mirror assembly and the new OEM assembly is over $400 → A used OEM assembly from a low-mileage vehicle is a reasonable option.
• If The failure is the wiring connector (pigtail) → Always buy a new pigtail. Used connectors have brittle wires or hidden corrosion.

Warranty tradeoff: A new aftermarket sensor has a 1-year to lifetime warranty. A used assembly has a 30-90 day warranty. An OEM part installed by a dealer has a 1-2 year warranty.

Worst-case if a used part fails: $150-$250 if a used mirror assembly's integrated sensor fails, requiring repeat labor.

What Happens If You Wait — Timeline

1. 0-1 month: Check Engine Light illuminates. Dashboard displays -40°F. Automatic climate control functions are disabled. (MPG impact: 0-5%% · Added cost: $0)
2. 1-4 months: Engine consistently runs a richer fuel mixture to compensate for the perceived extreme cold, decreasing fuel economy. (MPG impact: 5-10%% · Added cost: $50-$150 in wasted fuel.)
3. 4-12 months: Prolonged rich exhaust degrades catalytic converter efficiency and causes O2 sensors to become sluggish. (MPG impact: 5-10%% · Added cost: $200-$500 (potential O2 sensor replacement))
4. 12+ months: Sustained overheating from the rich mixture melts the catalyst substrate, leading to complete catalytic converter failure. (MPG impact: 10-15%% · Added cost: $1200-$2800 (catalytic converter replacement))

Cost of Not Fixing It

• 0-3 months: Incorrect temperature display, disabled automatic climate control, and a 5-10% drop in fuel economy due to a richer fuel mixture. (Added cost: $10-$30 per month in wasted fuel.)
• 3-12 months: Prolonged rich running condition increases carbon buildup on spark plugs and O2 sensors, stressing the catalytic converter. (Added cost: $200-$500 for potential O2 sensor or spark plug replacement.)
• 12+ months: Significant risk of catalytic converter failure due to constant overheating from the rich exhaust mixture. (Added cost: $1200-$2800 for catalytic converter replacement.)

Diagnosis Steps

1. Read the Code and Review Live Data
   Use an OBD-II scanner to confirm P0073. Navigate to the live data stream and observe the 'Ambient Air Temperature' PID. A reading of -40°F confirms the open circuit fault. Compare the AAT reading to the Intake Air Temperature (IAT) on a cold engine; they should be nearly identical.
   Tools: OBD-II Scanner (Beginner)
2. Locate and Visually Inspect the Sensor and Harness
   Find the AAT sensor behind the front grille, on a radiator support bracket, or inside a side mirror. Look for obvious damage: broken wires, a disconnected plug, or heavy corrosion.
   Tools: Flashlight (Beginner)
3. Inspect the Electrical Connector
   Unplug the sensor and inspect the metal pins inside both the sensor and the wiring harness connector. Look for green or white corrosion, bent pins, or water intrusion.
   Tools: None (Beginner)
4. Pro Tip: Perform a Jumper Wire Test
   To instantly isolate the sensor from the wiring, leave the sensor unplugged and insert a small jumper wire (or paperclip) between the two pins inside the wiring harness connector. With the key on, watch the AAT live data on your scanner. If the temperature swings from -40°F to a very high temperature, the wiring and PCM are perfect, and the sensor is dead. If it stays at -40°F, the wiring is broken.
   Tools: Jumper Wire, OBD-II Scanner (Intermediate)
5. Test the Harness for Reference Voltage and Ground
   With the sensor unplugged and the key 'On' (engine off), set your multimeter to DC Volts. Connect the black probe to the negative battery terminal. Touch the red probe to each pin inside the harness connector. One wire must show a 5-volt reference signal, and the other must read near 0 volts (ground). No voltage indicates a broken wire back to the PCM.
   Tools: Multimeter (Intermediate)
6. Test the Sensor's Resistance
   Set a multimeter to Ohms (Ω). Touch the probes to the two pins on the AAT sensor. A good thermistor shows specific resistance (e.g., ~10,000 ohms at 77°F). If the multimeter reads 'OL' (Over Limit), the sensor is internally broken and requires replacement.
   Tools: Multimeter (Intermediate)
7. Pro Tip: Check for a Short to Voltage
   With the sensor disconnected and key on, test the signal wire with a multimeter set to DC Volts. If it reads significantly above 5 volts (e.g., 12 volts), the signal wire has chafed and is touching a power wire, causing a 'short to voltage' that triggers P0073.
   Tools: Multimeter (Advanced)
8. Pro Tip: Perform a Voltage Drop Test on the Ground Circuit
   If you have 5 volts on the reference wire but the jumper test fails, check for a bad ground. Reconnect the sensor. Set your multimeter to a low DC Volts scale. Connect the red probe to the ground wire at the back of the sensor connector and the black probe to the negative battery terminal. With the key on, the reading must be under 0.1 volts. Higher readings indicate a bad ground.
   Tools: Multimeter (Advanced)
9. Advanced: Correlate Voltage and Resistance to Temperature
   Use a multimeter with a temperature probe. A typical AAT sensor has a predictable resistance curve: ~336,000 Ohms at -40°F, 10,000 Ohms at 77°F, and 2,000 Ohms at 122°F. Warm the sensor with a hairdryer; the resistance must drop smoothly. Sudden jumps or an 'OL' reading confirms failure.
   Tools: Multimeter with Temperature Probe, Heat Gun/Hairdryer, Service Manual (Advanced)
10. Advanced: Analyze Live Data Voltage Thresholds
    Using a professional scan tool, monitor the AAT sensor voltage PID directly. Normal operating range is 0.5V to 4.8V. P0073 triggers when the PCM sees voltage above 4.9V for a few consecutive seconds. Seeing 5.0V confirms an open circuit.
    Tools: Professional OBD-II Scanner (Advanced)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: Varies (often set on startup) (The PCM performs a rationality check on a cold start, comparing AAT, IAT, and ECT. If AAT is wildly different, the code sets immediately.)
• AAT Sensor Voltage: > 4.9 Volts (The primary trigger. The PCM sees a voltage higher than the sensor's maximum possible reading, confirming an open circuit.)
• Engine Load: 15-35% (The code sets during steady-state driving, not necessarily under heavy load.)
• Vehicle Speed: Any (Sets while idling or at highway speeds as the check is continuous.)

Related Codes

• P0072 — The opposite of P0073. P0072 (Circuit Low) is triggered by a short to ground, causing an abnormally low voltage signal and an extremely high temperature reading.
• P0113 — Intake Air Temperature (IAT) Sensor Circuit High. Compare AAT and IAT readings on a cold engine. If P0073 is active, the AAT reads -40°F while the IAT shows a plausible ambient temperature, isolating the fault to the AAT circuit.
• B1255 — On many Ford vehicles, the AAT sensor reports to the Body Control Module (BCM). An open circuit sets body code B1255 (Ambient Air Temp Sensor Open) instead of, or alongside, P0073.
• P0070 — A general fault code for the AAT sensor circuit, indicating a malfunction without specifying if the voltage is high, low, or intermittent.

Climate & Environmental Factors

• Cold Climates with Road Salt: Road salt is highly corrosive and attacks the AAT sensor's wiring and connector pins. This corrosion causes the open circuit that triggers P0073, making it a frequent failure in winter states.
• High Humidity / Heavy Rain: Moisture penetrates non-sealed connectors or damaged wire insulation, accelerating corrosion and leading to high-resistance open circuits.
• Extreme Heat: Prolonged exposure to extreme heat makes wire insulation brittle and prone to cracking, exposing the copper wire to the elements and causing shorts.

How to Talk to a Mechanic About This Code

Say this: "I have a P0073 code for the ambient air temperature sensor and my dash reads -40 degrees. I'd like to schedule a diagnostic to determine if the failure is the sensor itself, the connector, or the wiring harness."

This signals you have done basic research and focuses the technician on a specific, efficient diagnostic path (testing the circuit) rather than open-ended exploration.

Avoid saying:

• 'My check engine light is on, can you look at it?'
• 'My A/C isn't working.'
• 'Just fix whatever is wrong.'

Questions to ask before authorizing the repair:

• Did you perform a jumper wire test to confirm the wiring and PCM are good?
• If the wiring is damaged, how will you ensure the repair is weatherproof and durable?
• Can you show me the failed part and explain the test that confirmed its failure?
• What is the warranty on the parts and labor for this specific repair?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Recommended if the sensor is in a mirror and you suspect a complex wiring issue, or if under warranty. Otherwise, an independent shop is more cost-effective.
  Best for: Vehicles under warranty, Complex wiring issues on newer cars with sensors in mirrors (Ford/Ram), Diagnosing very rare control module (PCM/BCM) faults
  Downsides: Highest labor rates, often 1.5-2x more than independent shops., May prefer replacing an entire assembly (e.g., full mirror) when a smaller repair is possible. (Typical cost: +50% vs. baseline)
• Independent Shop: Best fit for most P0073 situations. This is a routine electrical diagnosis that any competent independent shop handles efficiently.
  Best for: Out-of-warranty vehicles where cost is a factor., Diagnosing and repairing common electrical faults like a bad sensor or broken wire.
  Downsides: Quality varies greatly. Vet shops by checking for ASE certifications and online reviews., May lack expensive, manufacturer-specific tools for rare module programming. (Typical cost: +0% vs. baseline)
• Chain Shop: Use with caution. Acceptable if you have already diagnosed a failed sensor, but AVOID for initial diagnosis of an electrical problem.
  Best for: Simple part replacement when you are certain the sensor itself has failed.
  Downsides: Technician skill varies dramatically; may lack diagnostic experience for wiring faults., High pressure to upsell can lead to replacing parts that are not the root cause. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 40-50% of the car's private-party value, pause and reconsider the repair.

• Car worth $4000, fix is $250: Fix it. The repair cost is minor compared to the car's value.
• Car worth $12000, fix is $300: Fix it. This is a routine repair, not a major expense.
• Car worth $2500, fix is $1200: Walk away. This repair cost is nearly 50% of the car's value and suggests a rare, complex problem (like a PCM failure) that isn't worth fixing.

What Scan Tool You Need for This Code

Minimum: Any OBD-II reader that displays Live Data (PIDs).

A basic $20 reader that only shows the code 'P0073' is insufficient. You must see the live data for the 'Ambient Air Temperature' PID to confirm it is stuck at -40°F.

Budget: BlueDriver Pro or Foxwell NT301 (~$90-120) — Reads/clears codes and displays the live Ambient Air Temperature reading needed for diagnosis.

Mid-range: Innova 5610 or Autel AL619 (~$100-320) — Provides live data graphing to visualize sensor behavior and reads ABS/SRS codes for general DIY use.

Professional: Autel MaxiCOM MK808S (~$450-550) — Offers full bidirectional control and access to manufacturer-specific body codes (like Ford's B1255). Professional-level overkill for just this one code.

Rent vs buy: For a one-time diagnosis, AutoZone offers a Loan-A-Tool program to borrow an OBD-II scanner for free. Buy a scanner only if you diagnose issues more than once a year.

How to Clear the Code After You Fix It

1. Use an OBD-II scan tool to clear active and pending codes.
2. Disconnecting the battery for 10-15 minutes also works but resets other vehicle memory.
3. Perform a complete drive cycle to allow the computer to verify the repair.

Drive cycle (~20 minutes): Cold start (engine temp below 122°F), idle for 2-3 minutes. Drive at a steady 55 mph for 5-10 minutes. Perform stop-and-go city driving for 5-10 minutes. Let the vehicle cool down completely.

Readiness monitors affected: Comprehensive Component Monitor, Catalyst and O2 sensor monitors (if the rich condition persists)

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Clearing the code without fixing the broken wire results in the code returning instantly.
• Clearing the code does not erase a 'Permanent DTC'. The vehicle must complete a self-test drive cycle.
• Some vehicles require a specific scan tool procedure to reset learned temperature values after replacement.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An illuminated Check Engine Light is an automatic failure. Readiness monitors must be 'Ready', requiring a drive cycle after repair.
• New York: Fails the NYS OBD-II inspection if the Malfunction Indicator Light is on for any emissions-related fault code like P0073.
• Texas: In emissions-testing counties, an illuminated Check Engine Light is an automatic failure. You cannot pass until the repair is made and the code clears.

Most Commonly Affected Vehicles

• Dodge / Ram / Jeep / Chrysler Ram 1500/2500/3500, Grand Cherokee, Wrangler (2010-2024) — Extremely common. On 2013+ Ram trucks, the sensor is in the driver's side mirror. Installing aftermarket tow mirrors without a sensor provision guarantees this code; a special harness is needed. On Wranglers, the sensor is behind the grille and vulnerable to off-road damage.
• Ford F-150, F-250/F-350 Super Duty, Transit Connect (2015-2025) — On mid-2018+ F-150s and Super Duty trucks, the sensor is in the passenger-side mirror. Cheap aftermarket mirrors are a common cause. A TSB (25-2545) exists for 2023-2025 Super Duty trucks. Fords may log a Body code (B1255) instead of P0073.
• Chevrolet / GMC Silverado, Sierra, Cruze, Equinox (2014-2024) — GM software disables the A/C compressor clutch entirely when P0073 is active, making 'no A/C' the primary complaint. On 2019+ trucks, wiring damage under the air intake box is a known cause.
• BMW 3-Series (E90/F30), 5-Series, X3, X5 (2006-2018) — A well-known pattern failure. The sensor is located in the lower front bumper liner, making its wiring highly susceptible to damage from road debris and snow/ice buildup.
• Nissan Altima, Sentra, Maxima, Rogue (2007-2024) — Common across the Nissan lineup. The issue is frequently a failed sensor located behind the front bumper near the hood latch support.
• Hyundai / Kia Genesis Coupe, Tucson, Optima, Sorento (2011-2020) — On some models, the PCM defaults to a fixed value of 68°F (20°C) when a fault is detected, rather than -40°F.
• Subaru Impreza, Outback, Forester (2015-2024) — The AAT sensor is located directly behind the front bumper cover and is susceptible to wiring harness damage from minor impacts.
• Volkswagen / Audi Jetta, Golf, Passat, A4 (2008-2020) — Typically caused by a faulty sensor or damaged wiring near the front of the vehicle, immediately disabling climate control.

Manufacturer-Specific Notes

• Dodge / Ram / Chrysler: The AAT sensor is in the driver's side mirror on most 2013+ Ram trucks. Installing aftermarket tow mirrors lacking the sensor guarantees P0073. The fix requires a special add-on harness.
• Ford: On mid-2018+ F-150s and Super Duty trucks, the sensor is in the passenger-side mirror. The system frequently sets Body code B1255 instead of Powertrain code P0073.
• Jeep: On Wranglers, the sensor's exposed position behind the grille makes it a common casualty of off-roading. A P0073 fault disables the auto start/stop system and, if the harness shorts, causes turn signal malfunctions.
• General Motors (Chevy/GMC): GM's software logic disables the A/C compressor clutch entirely when P0073 is active as a protective measure, making 'A/C blows warm' the primary symptom.

Real Owner Stories

2017 Ram 1500 with P0073 after mirror swap

Owner installed aftermarket tow mirrors and immediately got a Check Engine Light with code P0073 and a -40°F reading.

What they tried:

1. Clearing the code, which returned instantly.
2. Checking fuses, which were all good.

Outcome: The aftermarket mirrors lacked a provision for the factory AAT sensor. The owner installed an add-on sensor harness (Boost Auto Parts P/N 2843) that wires into the mirror's main connector, resolving the code.

Lesson: On Ram and Ford trucks, the AAT sensor is in a side mirror. If you replace a mirror, ensure the new one has a compatible sensor or buy a relocation harness.

2012 Jeep Wrangler JK with P0073 and turn signal failure

After an engine swap, the Jeep had a P0073 code, a -40°F temp reading, and rapidly flashing front turn signals.

What they tried:

1. Replacing the AAT sensor, which did not fix the problem.
2. Replacing a turn signal bulb, which did not fix the problem.
3. Visually inspecting the TIPM fuse box.

Outcome: Diagnosed as a short-to-voltage in the wiring harness where the AAT sensor and turn signal circuits run together. Damage during the engine swap caused the AAT signal wire to contact a power wire. Tracing and repairing the harness fixed both issues.

Lesson: If another electrical system fails simultaneously with the AAT sensor, suspect a wiring harness issue. The two problems share a single point of damage.

2018 Chevrolet Equinox with an easy fix

The Check Engine Light came on, the dash showed -40°F, and the A/C blew warm air. The owner suspected a major A/C compressor failure.

What they tried:

1. The owner first suspected a refrigerant leak.

Outcome: A visual inspection behind the front grille revealed the AAT sensor was simply unplugged, likely dislodged by road debris. Reconnecting the sensor and clearing the code restored A/C function immediately.

Lesson: Always start with a visual inspection. Before buying parts, ensure the sensor is actually plugged in.

How to Prevent This Code From Triggering

• Apply Dielectric Grease to Connector (Any time sensor is replaced or connector is serviced) — Dielectric grease seals electrical connectors from moisture, dirt, and road salt, preventing the pin corrosion that causes the 'circuit high' open circuit.
• Secure Wiring Harness with Zip Ties (During any under-hood or front-end maintenance) — Securing the harness prevents the insulation from chafing against sharp metal edges, which leads to broken wires or shorts to voltage.
• Periodically Rinse Front Grille and Bumper Area (Monthly, especially in winter road salt areas) — Rinsing removes accumulated road salt and mud, preventing a corrosive poultice from destroying the sensor and its connector.
• Use Heat-Shrink Connectors for Wire Repairs (When repairing any damaged wiring) — Heat-shrink butt connectors contain a sealant that creates a waterproof bond, essential for a circuit exposed to the elements.
• Inspect Connector During Routine Maintenance (Every oil change or tire rotation) — A visual inspection catches early signs of corrosion (white or green powder), allowing for simple cleaning before it triggers a Check Engine Light.

Frequently Asked Questions

Why does my dash say it's -40°F outside?

When the computer detects an open circuit (P0073), it rejects the invalid signal. As a failsafe, it displays a default, out-of-range value, which is -40°F on most vehicles.

I replaced the AAT sensor, but the P0073 code came back. What now?

This means the fault is in the wiring or connector, not the sensor. Use a multimeter to test for a 5-volt reference and good ground at the connector. A jumper wire test quickly confirms if the wiring back to the PCM is intact.

Can P0073 cause the vehicle to go into 'limp mode'?

It is extremely rare. However, if the computer enriches the fuel mixture enough to cause a severe misfire, it triggers a flashing check engine light and limp mode to protect the catalytic converter.

How much does it cost to fix code P0073?

A professional diagnosis costs $100-$150. Replacing the sensor costs $65-$200 including parts and labor, while repairing a broken wire typically costs $100-$200.

My turn signals and AAT sensor failed at the same time. Are they related?

Yes, particularly on vehicles like the Jeep Wrangler. The AAT sensor wiring bundles with the front turn signal harness, so a single point of damage or a short affects both systems simultaneously.

Will a blown fuse cause P0073?

Yes. On many 2013-2018 Dodge Ram trucks, a 10-amp fuse (F99) powers the temperature sensor circuit, and a blown fuse creates an open circuit.

What does a 'permanent' P0073 code mean?

A permanent DTC is stored in memory and cannot be erased with a standard scanner. The vehicle's computer must verify the fault is fixed by completing a specific drive cycle before it clears the code.

Key Takeaways

• P0073 triggers when the computer sees an open circuit in the ambient temperature sensor, causing the dashboard to display a default -40°F.
• The most common cause is a damaged wire or corroded connector behind the front grille, not a failed sensor.
• On 2013+ Ram and 2015+ Ford trucks, installing aftermarket tow mirrors without a built-in sensor guarantees this code; fixing it requires a $30-$40 relocation harness.
• Before buying parts, perform a jumper wire test at the sensor connector: if the live data temperature jumps from -40°F to a high value, the wiring is good and the sensor is bad.