If your OBD-II scanner displays P0073, your vehicle’s Engine Control Module (ECM), Powertrain Control Module (PCM), Body Control Module (BCM), or another control module has detected higher-than-expected voltage in the ambient air temperature sensor circuit.
The generic OBD-II definition for P0073 is:
Ambient Air Temperature Sensor Circuit High
Depending on the manufacturer or scan tool, the description may appear as:
- Ambient Air Temperature Sensor Circuit High
- Ambient Air Temperature Sensor Circuit “A” High
- Outside Air Temperature Sensor Circuit High
- Ambient Temperature Sensor Signal High
- Ambient Air Temperature Sensor Open Circuit
- Ambient Temperature Sensor Short to Voltage
Ford’s official OBD documentation identifies P0073 as an ambient air temperature sensor circuit-high fault. Some manufacturer diagnostic procedures describe the condition as a circuit that is open or shorted to battery voltage.
The ambient air temperature sensor measures the temperature outside the vehicle. Its signal may be used by the:
- PCM
- BCM
- Instrument cluster
- HVAC control module
- Driver-door module
- Diesel engine controller
- Automatic climate-control system
P0073 is commonly caused by:
- Disconnected ambient temperature sensor
- Open sensor circuit
- Broken wire
- Corroded connector
- Failed ambient air temperature sensor
- Signal circuit shorted to voltage
- Front bumper or mirror damage
- Loose electrical connector
- Incorrect replacement sensor
- Control-module or communication fault
Because most ambient temperature sensors use a negative-temperature-coefficient thermistor, an open circuit or high signal voltage is often interpreted as an extremely cold outside temperature.
Possible symptoms include:
- Check Engine Light
- Outside-temperature display showing
-40°For another minimum value - Missing exterior-temperature display
- Automatic climate-control problems
- Air conditioning disabled or limited
- Heater or defroster operating incorrectly
- Heated mirrors activating unexpectedly
- Remote-start climate-control problems
- Stop-start system disabled
- No noticeable drivability symptoms
For additional diagnostic information, visit:
P0073 Quick Facts
| Item | Information |
|---|---|
| OBD-II Code | P0073 |
| Description | Ambient Air Temperature Sensor Circuit High |
| Category | Powertrain |
| System | Fuel and Air Metering |
| Main Component | Ambient Air Temperature Sensor |
| Fault Type | High Circuit Voltage |
| Common Electrical Cause | Open Circuit or Disconnected Sensor |
| Severity | Low to Moderate |
| Safe to Drive? | Usually |
| Typical Repair Cost | $50–500 |
What Does P0073 Mean?
P0073 means the control module sees voltage in the ambient air temperature sensor circuit that is above the expected operating range.
The ambient air temperature sensor is usually a thermistor whose resistance changes with temperature.
In a typical negative-temperature-coefficient circuit:
- Cold temperature increases sensor resistance
- Warm temperature decreases sensor resistance
- Higher resistance causes the signal voltage to rise
- An open circuit creates effectively infinite resistance
- The module may interpret the open circuit as extreme cold
When the sensor is disconnected or a wire breaks, the module may see the pull-up voltage with little or no current flowing through the sensor.
This may cause:
- P0073
- A minimum exterior-temperature display
- Climate-control problems
- Missing ambient-temperature information
Ford documentation lists P0073 as a continuously monitored ambient-temperature circuit-high fault on certain diesel applications.
What Is the Ambient Air Temperature Sensor?
The ambient air temperature sensor measures the temperature of the air surrounding the vehicle.
It may be used for:
- Exterior-temperature display
- Automatic heating and air conditioning
- Windshield-defrost strategy
- Cold-start calculations
- Cooling-fan operation
- Diesel glow-plug control
- Turbocharger calculations
- Heated mirror operation
- Remote-start climate settings
- Stop-start system operation
- Emissions monitoring
The sensor is typically mounted where it can receive outside airflow while avoiding excessive heat from the engine and radiator.
Common locations include:
- Behind the front grille
- In front of the radiator
- Near the air-conditioning condenser
- Behind the front bumper
- Near the hood-latch support
- Inside a lower bumper opening
- Inside a side mirror
Some vehicles route the ambient-temperature signal through the BCM, instrument cluster, or door module before sending the data to the PCM.
How the Ambient Air Temperature Sensor Works
Most ambient air temperature sensors are negative temperature coefficient thermistors, also called NTC thermistors.
A typical sensor uses two circuits:
- Signal or bias-voltage circuit
- Sensor-return or ground circuit
The control module supplies voltage through an internal resistor.
The sensor changes the circuit resistance according to temperature.
With a typical NTC sensor:
- Low temperature = high resistance
- High temperature = low resistance
- High resistance = higher signal voltage
- Low resistance = lower signal voltage
The module converts the measured voltage into an outside-temperature value.
The exact resistance, voltage, and calculated-temperature values vary by vehicle.
What Does “Circuit High” Mean?
“Circuit high” means the control module is receiving more voltage than expected on the sensor signal circuit.
It does not mean:
- The outside temperature is high
- Engine temperature is high
- Battery voltage is necessarily high
- Refrigerant pressure is high
It refers specifically to the ambient temperature sensor’s electrical signal.
Common circuit-high causes include:
- Open sensor
- Disconnected sensor
- Broken signal wire
- Broken sensor-return wire
- Loose connector
- Corroded terminal
- Signal circuit shorted to voltage
- Incorrect connector pinout
- Failed module input circuit
On many vehicles, a circuit-high condition causes the reported outside temperature to become extremely low.
Why P0073 May Display Minus 40 Degrees
An open circuit can cause the control module to see maximum signal voltage.
Because high resistance corresponds to cold temperature in many NTC circuits, the module interprets the signal as extreme cold.
The display may show:
-40°F-40°C- Dashes
- A blank reading
- Another manufacturer-specific minimum value
Minus 40 is especially common because it is the same temperature on both Fahrenheit and Celsius scales.
A dashboard showing minus 40 during a summer heat wave is usually not predicting an exciting weather event. It is announcing that the sensor circuit has stopped participating.
P0070 vs P0071 vs P0072 vs P0073
| Code | Description | Typical Meaning |
| P0070 | Ambient Air Temperature Sensor Circuit | General circuit malfunction |
| P0071 | Ambient Air Temperature Sensor Range/Performance | Implausible or slow reading |
| P0072 | Ambient Air Temperature Sensor Circuit Low | Low signal voltage, often short to ground |
| P0073 | Ambient Air Temperature Sensor Circuit High | High signal voltage, often open circuit |
| P0074 | Ambient Air Temperature Sensor Circuit Intermittent | Signal changes or drops out unpredictably |
In a typical NTC circuit:
- P0072 may produce an extremely hot reading
- P0073 may produce an extremely cold reading
Manufacturer circuit logic can differ, so always verify the vehicle’s wiring diagram and test procedure.
How the PCM Detects P0073
The monitoring module checks the ambient-temperature signal for an electrical value above its programmed limit.
P0073 may be stored when:
- Signal voltage exceeds the calibrated threshold
- Sensor resistance is too high
- The sensor circuit is open
- The sensor is disconnected
- The signal circuit is shorted to battery voltage
- Ambient-temperature data is unavailable
- Another module reports an ambient sensor circuit-high failure
- The fault remains present for a specified time
Some Ford applications monitor the ambient-temperature circuit continuously and can identify a high-circuit fault within a short monitoring period.
Other applications may require:
- Multiple ignition cycles
- A minimum vehicle speed
- Several minutes of driving
- A valid temperature message from another module
A technical bulletin for certain vehicles notes that ambient temperature may be missing or inaccurate and may require driving above 15 mph for several minutes after repair before the displayed value updates.
Symptoms of P0073
Possible symptoms include:
- Check Engine Light
- Outside-temperature display reading extremely cold
- Temperature display stuck at its minimum value
- Exterior-temperature display showing dashes
- Missing ambient-temperature display
- Automatic climate control operating incorrectly
- Air conditioning disabled
- Air conditioning limited in cold-weather mode
- Heater output behaving incorrectly
- Windshield-defrost operation affected
- Heated mirrors activating unnecessarily
- Remote-start climate system behaving incorrectly
- Stop-start system disabled
- Diesel cold-start strategy affected
- Additional ambient-temperature codes
- No noticeable engine-performance symptoms
P0073 often has little effect on basic drivability.
The vehicle may continue to:
- Start normally
- Idle normally
- Accelerate normally
- Shift normally
- Maintain normal engine temperature
The most noticeable symptom may be an outside-temperature display attempting to convince the driver that northern Alaska has relocated behind the front grille.
Can P0073 Affect Air Conditioning?
Yes.
The automatic climate-control system may use ambient temperature to determine:
- Whether the air-conditioning compressor should operate
- How much cooling is required
- Whether automatic defrost should activate
- Whether outside air is cold enough to limit compressor operation
- How the blower and blend doors should respond
- Whether heated mirrors should operate
When the module believes outside temperature is extremely cold, it may:
- Disable compressor operation
- Limit air-conditioning output
- Increase heater demand
- Alter recirculation strategy
- Activate cold-weather features
This may create poor cabin cooling even when the air-conditioning system itself is mechanically healthy.
Can P0073 Affect Engine Performance?
P0073 usually does not create severe engine-performance problems.
However, ambient-temperature information may contribute to:
- Cold-start fueling
- Idle-speed strategy
- Diesel glow-plug operation
- Cooling-fan control
- Turbocharger calculations
- Air-density compensation
- Stop-start operation
- Emissions-monitor enable conditions
Possible secondary effects include:
- Slightly difficult starting
- Longer warm-up strategy
- Poor fuel economy
- Disabled stop-start system
- Incomplete emissions monitors
- Reduced-power operation on certain applications when other faults are present
A 2026 service bulletin lists P0073 among active or stored faults on a specific vehicle application, illustrating that the code can also appear as part of a broader module or electrical problem.
Common Causes of P0073
1. Disconnected Ambient Air Temperature Sensor
A disconnected sensor is one of the most common causes of P0073.
The connector may have been left unplugged during:
- Bumper replacement
- Grille replacement
- Radiator service
- Condenser replacement
- Headlight repair
- Fog-light installation
- Collision repair
- Mirror replacement
With the sensor unplugged, the module may see full pull-up voltage and interpret the circuit as open.
2. Open Ambient Temperature Sensor
The sensor may fail internally and develop an open circuit.
Possible causes include:
- Age
- Internal corrosion
- Moisture intrusion
- Thermal cycling
- Road-debris impact
- Manufacturing defect
- Broken internal connection
An open sensor will often measure infinite resistance with a multimeter.
3. Broken Signal Wire
The signal wire may break because of:
- Front-end collision
- Harness tension
- Improper routing
- Sharp bumper brackets
- Vibration
- Rodent damage
- Previous repairs
- Corrosion inside the insulation
The insulation may look intact even when the conductor inside is broken.
4. Broken Sensor-Return Wire
An open return or ground circuit can also interrupt current flow through the sensor.
This may create the same electrical result as:
- Disconnected sensor
- Open sensor
- Broken signal wire
Test both wires rather than assuming the signal wire is always at fault.
5. Loose Electrical Connector
A connector that is not fully seated may create intermittent or permanent loss of sensor contact.
Possible causes include:
- Broken locking tab
- Connector not pushed in fully
- Incorrect connector
- Bumper movement
- Loose terminal fit
- Missing secondary lock
A technical bulletin involving certain trucks identifies a loose ambient-temperature sensor connector as a likely cause of P0073.
6. Corroded Connector Terminals
Corrosion can increase circuit resistance or completely interrupt the connection.
Inspect for:
- Green corrosion
- White oxidation
- Water
- Road salt
- Loose terminals
- Bent pins
- Damaged seals
- Broken connector housing
A service bulletin for certain vehicles instructs technicians to inspect an A-pillar or door connector for corrosion, bent terminals, or spread terminals when P0073 is stored.
7. Water Intrusion
The sensor’s forward or mirror-mounted location makes it vulnerable to water.
Moisture may enter through:
- Damaged connector seal
- Cracked sensor
- Unsealed wiring splice
- Mirror housing
- Door connector
- Damaged bumper harness
Water may produce:
- Corrosion
- Intermittent open circuit
- High resistance
- Signal dropouts
- P0073 after rain or washing
8. Front-End Collision Damage
The ambient sensor is frequently located behind the front bumper or grille.
Even a minor impact can cause:
- Broken sensor
- Severed wiring
- Crushed connector
- Missing bracket
- Stretched harness
- Sensor left disconnected
- Incorrect repair routing
Always ask whether the vehicle recently received front-end body work.
9. Sensor Missing After Bumper Repairs
The sensor may have been:
- Removed with the damaged bumper
- Left attached to the old grille
- Forgotten during reassembly
- Tucked behind the bumper
- Installed on an incorrect harness
- Omitted from an aftermarket bumper
The dashboard may then display its coldest possible reading despite the sensor enjoying retirement somewhere in the body shop.
10. Signal Circuit Shorted to Voltage
The signal wire may contact:
- Battery-positive wiring
- Ignition-voltage circuit
- Headlight wiring
- Fog-light wiring
- Accessory power
- Incorrect splice
Some manufacturer fault descriptions specifically associate P0073 with a circuit that is open or shorted to battery voltage.
11. Incorrect Previous Wiring Repair
Poor repairs may include:
- Unsealed butt connectors
- Twisted wires
- Electrical tape only
- Incorrect wire gauge
- Weak crimp
- Cold solder joint
- Wire colors matched incorrectly
- Connector terminals installed in the wrong cavities
An open or high-resistance repair can return after:
- Rain
- Vibration
- Temperature changes
- Bumper movement
Use weather-sealed automotive repair methods.
12. Incorrectly Pinned Replacement Connector
A replacement pigtail may have:
- Signal and return reversed
- Wrong terminal locations
- Loose terminal locks
- Poor crimping
- Incorrect connector type
Compare terminal positions with the wiring diagram.
Matching wire colors is helpful, but not sufficiently scientific when the previous repair also matched wire colors incorrectly.
13. Damaged Mirror-Mounted Sensor
On vehicles with a mirror-mounted ambient temperature sensor, possible causes include:
- Broken mirror
- Incorrect replacement mirror
- Missing internal sensor
- Door-harness damage
- Mirror connector corrosion
- Water intrusion
- Broken door-jamb wire
- Door-module fault
The ambient sensor may be integrated into the mirror assembly or connected through a door module.
14. Incorrect Replacement Mirror
An aftermarket mirror may:
- Omit the ambient sensor
- Use an incompatible sensor
- Have a different connector
- Use a different resistance curve
- Lack the correct internal wiring
P0073 appearing immediately after mirror replacement strongly suggests inspecting the replacement assembly and connector.
15. Incorrect Replacement Sensor
An incorrect ambient sensor may have:
- Wrong resistance curve
- Excessively high resistance
- Different pinout
- Poor connector fit
- Incompatible calibration
- Internal open circuit out of the box
A new part is not automatically the correct part.
It may simply be a cleaner way to preserve the same trouble code.
16. Harness Damage Near Active Grille Shutters
Some vehicles route the ambient-temperature wiring near active grille shutters.
Possible problems include:
- Harness caught in moving shutters
- Wire stretched during grille service
- Connector left loose
- Chafing against the shutter frame
- Incorrect harness routing
Inspect the complete grille harness if the vehicle has active aerodynamic components.
17. Aftermarket Accessory Installation
Accessories installed near the front bumper may damage the sensor circuit.
Examples include:
- LED light bars
- Fog lights
- Grille lights
- Front cameras
- Parking sensors
- Snowplow wiring
- Radar equipment
Possible installation errors include:
- Screw through the harness
- Wire cut during drilling
- Sensor circuit used as an accessory source
- Harness pinched beneath a bracket
- Poor splice into nearby wiring
18. Instrument Cluster or BCM Fault
On some vehicles, the ambient sensor connects to the:
- Instrument cluster
- BCM
- HVAC module
- Door module
That module then broadcasts the temperature to the PCM.
Volkswagen diagnostic information notes that P0073 may involve a high ambient-temperature error signal sent from the instrument cluster to the engine controller.
A sensor circuit may therefore be functional at one module while another module reports incorrect or missing information.
19. Network Communication Problem
A CAN communication fault may prevent valid ambient-temperature data from reaching the PCM.
Look for:
- U-series communication codes
- Offline BCM
- Cluster communication faults
- Door-module faults
- Gateway problems
- Water-damaged connectors
P0073 may be secondary to a network or module issue rather than a direct sensor failure.
20. PCM, BCM, or Module Software Issue
Control-module software may incorrectly interpret the ambient signal or fail to process updated data.
Possible corrections include:
- PCM calibration update
- BCM software update
- Instrument-cluster update
- Module reconfiguration
- Revised sensor or wiring procedure
Always check vehicle-specific technical service bulletins before replacing a control module.
21. Failed Control Module
A failed module input circuit can create a false high-voltage reading.
Possible affected modules include:
- PCM
- BCM
- Instrument cluster
- HVAC control module
- Door module
Module failure is uncommon.
Only suspect it after verifying:
- Sensor resistance
- Both sensor wires
- Connector condition
- Circuit isolation
- Data across multiple modules
- Available software updates
Replacing a PCM before checking whether the sensor is still attached to the bumper is diagnosis performed with impressive confidence and very little evidence.
Is P0073 Serious?
P0073 is generally considered a low- to moderate-severity code.
The vehicle will usually continue to:
- Start
- Run
- Accelerate
- Shift
- Drive normally
However, the code may affect:
- Automatic climate control
- Air-conditioning operation
- Windshield defrosting
- Heated mirrors
- Outside-temperature display
- Cooling-fan logic
- Stop-start operation
- Cold-weather engine strategy
- Emissions monitoring
P0073 becomes more important if:
- Windshield defrosting is inadequate
- Air conditioning is disabled
- Multiple electrical codes are present
- Wiring is loose near the cooling fan
- The vehicle enters reduced-power mode
- Collision damage affected additional components
- The BCM or another module is offline
Can You Drive With P0073?
You can usually drive with P0073 for a limited period.
The code normally does not indicate an immediate risk of internal engine damage.
You should use caution if:
- Windshield visibility is reduced
- Defrost operation is affected
- Cooling fans operate abnormally
- The vehicle has additional communication codes
- The front bumper harness is loose
- Wiring is contacting moving components
- The vehicle enters limp mode
The temperature display being wrong is inconvenient.
A severed harness hanging near the radiator fan deserves considerably more attention.
How to Diagnose P0073
Step 1: Scan All Available Modules
Do not scan only the engine computer.
Check the:
- PCM
- BCM
- HVAC module
- Instrument cluster
- Door modules
- Gateway module
Look for:
- P0070
- P0071
- P0072
- P0073
- P0074
- Communication codes
- HVAC sensor codes
- Door-module faults
- Intake-air-temperature codes
- Coolant-temperature codes
Record freeze-frame data before clearing anything.
Step 2: Check the Outside-Temperature Reading
Compare:
- Dashboard temperature
- PCM ambient-temperature PID
- BCM ambient-temperature PID
- HVAC module data
- Actual outside temperature
A reading at or near the minimum programmed value often suggests:
- Open sensor
- Disconnected connector
- Broken wire
- High circuit voltage
A blank display or dashes may also indicate unavailable sensor information.
Step 3: Determine Which Module Reads the Sensor
Use a wiring diagram to determine whether the sensor connects directly to the:
- PCM
- BCM
- Instrument cluster
- HVAC module
- Door module
This determines where voltage and continuity testing should begin.
Do not assume P0073 means the sensor is wired directly to the PCM.
Step 4: Locate the Ambient Temperature Sensor
Common locations include:
- Behind the grille
- Near the condenser
- Behind the front bumper
- Near the hood latch
- Inside a side mirror
Confirm the correct sensor before disconnecting anything.
A modern front bumper may also contain:
- Impact sensors
- Parking sensors
- Radar sensors
- Active-grille actuators
- Outside-temperature sensor
Only one of these should be tested with an ohmmeter because the dashboard thinks it is cold.
Step 5: Inspect Recent Repair Areas
Ask whether the vehicle recently received:
- Bumper repair
- Grille replacement
- Radiator service
- Condenser replacement
- Headlight work
- Fog-light installation
- Mirror replacement
- Front-camera installation
- Collision repair
If P0073 began immediately afterward, begin inspection in the disturbed area.
Step 6: Inspect the Sensor
Check for:
- Cracked housing
- Missing sensor
- Broken mounting clip
- Impact damage
- Corrosion
- Water intrusion
- Incorrect part
- Damaged terminals
A missing or physically broken sensor should be replaced.
Step 7: Inspect the Connector
Look for:
- Connector left unplugged
- Loose fit
- Broken lock
- Bent pins
- Backed-out terminals
- Corrosion
- Water
- Damaged seals
- Spread terminals
A manufacturer bulletin has identified loose ambient-temperature sensor connectors as a cause of P0073 on certain applications.
Step 8: Inspect the Wiring Harness
Follow the harness toward the body or control module.
Look for:
- Broken wires
- Stretched sections
- Chafing
- Pinched insulation
- Poor splices
- Exposed copper
- Missing retaining clips
- Damage near bumper brackets
- Damage near door hinges on mirror-mounted systems
Gently pull each wire near the connector.
A conductor broken inside its insulation may stretch even though the outer covering looks intact.
Step 9: Observe Scan Data While Disconnecting the Sensor
If the manufacturer’s procedure permits, monitor ambient-temperature data while disconnecting and reconnecting the sensor.
Possible results:
- Reading becomes extremely cold when disconnected: module and circuit response may be normal
- Reading remains extremely cold when connected: sensor or wiring may be open
- Reading changes when connector is moved: loose terminal or intermittent circuit
- Reading differs across modules: communication or module problem
Because P0073 is already a likely open-circuit condition, this test must be interpreted carefully.
Step 10: Measure Sensor Resistance
Disconnect the sensor and measure resistance across its terminals.
Compare the result with:
- Actual ambient temperature
- Manufacturer resistance chart
- Known-good sensor
Possible findings:
- Infinite resistance: open sensor
- Excessively high resistance: biased cold or failing sensor
- Correct resistance: continue wiring tests
- Near-zero resistance: more consistent with circuit-low behavior
Step 11: Heat and Cool the Sensor
Apply controlled temperature changes using:
- Cool air
- Warm air
- Temperature-controlled environment
- Approved water-bath procedure
Monitor resistance.
A healthy NTC sensor should:
- Increase resistance as it cools
- Decrease resistance as it warms
- Change smoothly
- Remain within specification
A sensor that remains open at every temperature has completed its career.
Step 12: Check Bias or Pull-Up Voltage
With the sensor disconnected and ignition on, test circuit voltage according to the wiring diagram.
The module may provide:
- Five-volt bias
- Another regulated voltage
- Internal pull-up voltage
Do not assume every system uses exactly five volts.
Compare the reading with manufacturer specifications.
Step 13: Test the Signal Circuit for an Open
Disconnect the sensor and relevant control module as required.
Measure continuity from:
- Sensor connector
- Intermediate connector
- Control-module terminal
Look for:
- Infinite resistance
- Excessive resistance
- Intermittent continuity
- Broken splice
- Damaged connector terminal
Move the harness while watching the meter.
Step 14: Test the Return Circuit for an Open
Repeat continuity testing on the sensor-return or ground circuit.
An open return circuit can create the same symptoms as an open signal wire.
Do not stop after finding continuity on only one side of a two-wire sensor.
Step 15: Check for a Short to Voltage
With the sensor and module disconnected, inspect whether the signal circuit is receiving voltage from another source.
Possible sources include:
- Battery wiring
- Ignition wiring
- Headlight circuit
- Fog-light circuit
- Aftermarket accessory wiring
- Damaged bumper harness
Some manufacturer descriptions explicitly identify P0073 as a circuit-high, short-to-battery, or open condition.
Step 16: Check Connector Terminal Tension
A terminal can appear clean yet fail to grip the sensor pin.
Use the manufacturer-approved terminal test tool.
Look for:
- Spread terminal
- Loose fit
- Backed-out terminal
- Broken retaining tang
- Incorrect terminal size
Terminal-tension issues may create intermittent P0073 complaints.
Step 17: Perform a Wiggle Test
Monitor scan data while gently moving:
- Sensor connector
- Bumper harness
- Mirror harness
- Door-jamb wiring
- A-pillar connector
- Module connectors
Watch for:
- Temperature suddenly returning to normal
- Display changing to dashes
- Code status changing
- Intermittent communication loss
Certain service bulletins direct technicians to inspect door or A-pillar connectors for terminal and corrosion problems when P0073 is present.
Step 18: Substitute a Known Resistance
When approved by the manufacturer, install a resistor representing a known ambient temperature.
Then observe scan data.
If the module displays the expected temperature:
- Wiring and module are likely functional
- Original sensor is likely faulty
If the reading remains at extreme cold:
- Wiring may be open
- Terminal contact may be poor
- Wrong module may be reading the sensor
- Module input may be faulty
Use only the specified test resistance.
Step 19: Compare Ambient Data Across Modules
Check the value reported by:
- PCM
- BCM
- HVAC module
- Instrument cluster
- Door module
Possible findings:
- All modules show extreme cold: sensor or shared circuit fault
- BCM reads correctly but PCM does not: communication or programming issue
- Cluster alone is wrong: cluster display problem
- One module reports no signal: module or network fault
Step 20: Inspect Network Communication
If ambient-temperature information is transmitted over CAN, check for:
- U-series codes
- Offline module
- Gateway fault
- Door-module problem
- Cluster fault
- Corroded network connector
- Water intrusion
P0073 may be stored because the PCM received an error-status message rather than because it directly measured excessive sensor voltage.
Step 21: Inspect Aftermarket Accessories
Check installations near the front bumper or mirror.
Inspect:
- LED lights
- Light bars
- Fog lights
- Parking sensors
- Front cameras
- Snowplow wiring
- Radar equipment
- Replacement mirrors
Look for:
- Cut wires
- Drilled harnesses
- Incorrect splices
- Crushed wiring
- Shared connectors
Step 22: Check Technical Service Bulletins
Search manufacturer information using:
- VIN
- Model year
- Engine
- P0073
- Sensor location
- Mirror configuration
- Existing calibration number
Factory bulletins have documented P0073 complaints involving loose sensor connectors, corroded door connectors, missing ambient data, wiring faults, and specific repair procedures.
Step 23: Repair the Confirmed Fault
Possible repairs include:
- Reconnecting the sensor
- Replacing the ambient sensor
- Repairing an open signal wire
- Repairing the return circuit
- Replacing the connector
- Cleaning corrosion
- Repairing bumper wiring
- Replacing a mirror-mounted sensor
- Correcting connector pinout
- Repairing network communication
- Updating module software
Use weather-sealed automotive wiring repairs.
Step 24: Verify the Repair
After completing repairs:
- Clear all diagnostic trouble codes.
- Switch the ignition off.
- Allow the modules to power down.
- Restart the vehicle.
- Compare ambient temperature with actual conditions.
- Confirm the exterior-temperature display returns.
- Check HVAC operation.
- Road-test the vehicle.
- Drive at moderate speed if the display requires airflow to update.
- Complete the required drive cycle.
- Confirm P0073 does not return.
Some systems update slowly after the circuit is restored. Manufacturer guidance for certain vehicles requires several minutes of driving above approximately 15 mph before the ambient-temperature display updates.
Do not declare the repair unsuccessful thirty seconds after reconnecting the sensor while the vehicle remains parked beside a hot radiator.
Common Repairs and Costs
| Repair | Estimated Cost |
| Reconnect sensor or connector | $0–100 |
| Clean electrical connector | $50–150 |
| Replace ambient temperature sensor | $75–250 |
| Repair open wiring | $100–450 |
| Replace sensor connector | $75–275 |
| Repair front bumper harness | $150–600 |
| Repair door-jamb wiring | $150–700 |
| Replace mirror-mounted sensor | $150–600 |
| Replace complete mirror assembly | $300–1,500 |
| Diagnose network communication | $150–500 |
| Update PCM, BCM, or cluster software | $100–300 |
| Replace BCM or related module | $500–1,500+ |
| Replace PCM | $1,000–2,500+ |
Costs vary depending on:
- Sensor location
- Wiring accessibility
- Collision damage
- Mirror design
- Module programming
- Labor rate
- Diagnostic time
A disconnected sensor behind an open grille may take minutes to repair.
An open wire buried inside a heated, power-folding tow mirror with cameras and enough electronics to qualify as a small apartment may be less cooperative.
Common Diagnostic Mistakes
Avoid these common P0073 diagnostic mistakes:
- Assuming “circuit high” means high outside temperature
- Replacing the sensor without checking whether it is connected
- Ignoring recent bumper repairs
- Ignoring recent mirror replacement
- Testing only the signal wire and not the return wire
- Failing to inspect terminal tension
- Overlooking corrosion inside door connectors
- Confusing ambient temperature with intake-air temperature
- Assuming the sensor connects directly to the PCM
- Failing to scan the BCM and HVAC module
- Ignoring communication codes
- Installing an incorrectly calibrated aftermarket sensor
- Replacing a module before testing circuit continuity
- Clearing the code without verifying the displayed temperature
- Declaring failure before the filtered display has time to update
P0073 normally indicates a high electrical signal, not a warm day.
The dashboard may believe it is minus 40 outside because the sensor circuit is open—not because the weather has taken a sudden personal dislike to the driver.
Vehicles Commonly Affected
P0073 is a generic OBD-II code and may appear on many vehicle brands, including certain:
- Ford vehicles
- Lincoln vehicles
- Ram trucks
- Dodge vehicles
- Jeep models
- Chrysler vehicles
- Chevrolet vehicles
- GMC trucks
- Cadillac models
- Volkswagen vehicles
- Audi models
- BMW vehicles
- Mercedes-Benz vehicles
- Hyundai models
- Kia vehicles
- Mitsubishi models
- Commercial trucks
Application-specific P0073 issues documented in manufacturer service information include:
- Loose ambient sensor connectors
- Corroded A-pillar or door connectors
- Missing or inaccurate exterior-temperature data
- Open or short-to-battery circuits
- Mirror-mounted sensor faults
- Control-module software or data-message concerns
Always diagnose the exact vehicle rather than assuming every P0073 sensor is mounted behind the grille.
P0073 After Front Bumper Repairs
When P0073 appears after bumper, grille, radiator, or condenser work, inspect for:
- Sensor left disconnected
- Sensor missing
- Broken connector lock
- Wire pulled from terminal
- Harness stretched too tightly
- Harness pinched behind bumper
- Sensor attached to wrong bracket
- Incorrect bumper harness
- Accessory wiring damage
The repair history is often the fastest diagnostic tool available.
A code that appeared immediately after the bumper was removed is rarely asking the technician to begin by replacing the PCM.
P0073 After Mirror Replacement
On vehicles with mirror-mounted ambient sensors, inspect:
- Correct mirror part number
- Sensor included in mirror
- Mirror connector
- Door-jamb harness
- A-pillar connector
- Door module
- Network communication
A replacement mirror may fit the door perfectly while omitting the one inexpensive thermistor responsible for informing the entire vehicle what season it is.
P0073 in Wet Weather
P0073 that appears mainly after rain or washing may indicate:
- Connector water intrusion
- Damaged weather seal
- Corroded terminals
- Broken wire strands
- Moisture inside mirror housing
- Unsealed wiring splice
- Water-damaged body connector
Inspect the vehicle while the fault is active.
Electrical problems that depend on moisture frequently become model citizens after spending an afternoon drying inside a warm repair shop.
How to Prevent P0073
Reduce the likelihood of P0073 by:
- Reconnecting the sensor after bumper repairs
- Replacing broken connector locks
- Reinstalling factory wiring clips
- Protecting bumper wiring from sharp edges
- Using sealed automotive splices
- Keeping connector seals intact
- Inspecting the sensor after front-end impacts
- Using the correct replacement mirror
- Using the correct sensor part number
- Checking wiring after lighting installations
- Repairing water intrusion promptly
- Avoiding direct pressure-washer spray on damaged connectors
Frequently Asked Questions
What does P0073 mean?
P0073 means the control module has detected voltage above the expected range in the ambient air temperature sensor circuit.
What causes P0073 most often?
Common causes include:
- Disconnected ambient temperature sensor
- Open sensor
- Broken signal wire
- Broken return wire
- Loose connector
- Corroded terminals
- Signal wire shorted to voltage
Is P0073 serious?
P0073 is usually low to moderate in severity.
The vehicle normally remains drivable, but climate-control, defrost, exterior-temperature display, and temperature-dependent functions may be affected.
Can I drive with P0073?
Usually, yes.
Use caution if windshield defrost, cooling fans, or other temperature-dependent systems are not operating correctly.
Does circuit high mean the outside temperature is high?
No.
“Circuit high” means the electrical signal voltage is higher than expected.
On many vehicles, this causes an extremely low displayed temperature.
Why does my car show minus 40 degrees?
A display of -40°F or -40°C commonly indicates:
- Disconnected sensor
- Open sensor
- Broken wire
- High signal voltage
The exact fallback value varies by manufacturer.
Can a disconnected sensor cause P0073?
Yes.
A disconnected ambient air temperature sensor is one of the most common causes of P0073.
Can a bad ambient temperature sensor cause P0073?
Yes.
An internally open sensor can produce excessive circuit voltage.
Can broken wiring cause P0073?
Yes.
An open signal or return wire can interrupt current flow and set P0073.
Can bumper repairs cause P0073?
Yes.
The sensor may be disconnected, omitted, damaged, or have its wiring stretched during bumper repairs.
Can mirror replacement cause P0073?
Yes, on vehicles with a mirror-mounted ambient sensor.
An incorrect mirror may omit the sensor or use incompatible wiring.
Can corrosion cause P0073?
Yes.
Corrosion may increase resistance or create an open connection.
What is the difference between P0072 and P0073?
P0072 indicates low circuit voltage, commonly associated with a short to ground.
P0073 indicates high circuit voltage, commonly associated with an open circuit or disconnected sensor.
Can P0073 affect air conditioning?
Yes.
The HVAC system may disable or limit compressor operation if it believes outside temperature is extremely cold.
Can P0073 affect the heater?
Yes.
Automatic climate-control calculations may be inaccurate when ambient-temperature data is unavailable.
Can P0073 cause limp mode?
Usually not by itself.
Reduced-power operation is possible on some applications when P0073 appears with additional electrical, software, or module faults.
Does the ambient temperature sensor require programming?
The sensor itself usually does not require programming.
The vehicle may require:
- Code clearing
- Key cycle
- Several minutes of driving
- Temperature relearn
- Module reset
Replacement control modules may require programming.
How much does P0073 cost to fix?
A simple reconnection may cost little or nothing.
Sensor replacement often costs approximately $75–250, while wiring, mirror, network, or module repairs may cost several hundred dollars or more.
Final Thoughts
The P0073 code means the vehicle has detected high voltage in the ambient air temperature sensor circuit.
The most common causes include:
- Disconnected ambient temperature sensor
- Open sensor
- Broken signal wire
- Broken return circuit
- Loose connector
- Corroded terminals
- Front bumper damage
- Mirror wiring damage
- Signal wire shorted to voltage
- Control-module or communication problem
Start diagnosis by checking the exterior-temperature display.
If it shows an impossibly cold temperature:
- Locate the ambient sensor.
- Confirm it is connected.
- Inspect the connector and wiring.
- Measure sensor resistance.
- Test both circuit wires for continuity.
- Check for a short to voltage.
- Compare ambient-temperature data across modules.
- Review manufacturer technical service bulletins.
Do not confuse “circuit high” with “temperature high.” P0073 generally means signal voltage is high, and on many thermistor circuits that makes the vehicle believe it has been abandoned somewhere beyond the Arctic Circle.
Fortunately, the actual repair is often considerably warmer and simpler: reconnect a forgotten sensor, repair one broken wire, or replace a corroded two-pin connector hiding behind the bumper.
Related Articles
Ambient Air Temperature Sensor Codes
- P0070 Code Explained: Ambient Air Temperature Sensor Circuit
- P0071 Code Explained: Ambient Air Temperature Sensor Range/Performance
- P0072 Code Explained: Ambient Air Temperature Sensor Circuit Low
- P0074 Code Explained: Ambient Air Temperature Sensor Circuit Intermittent
Previous P-Code Articles
- P0070 Code Explained: Ambient Air Temperature Sensor Circuit
- P0071 Code Explained: Ambient Air Temperature Sensor Range/Performance
- P0072 Code Explained: Ambient Air Temperature Sensor Circuit Low
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