The P0073 trouble code is a diagnostic code that indicates an issue with the Ambient Air Temperature (AAT) sensor circuit in a vehicle. This code specifically points to a high input problem, suggesting that the sensor or its circuit is reporting a temperature that is higher than expected or outside the normal operating range.
| P0073 Code Meaning | P0073 Code Common Causes |
|---|---|
| Ambient Air Temperature Sensor Circuit High Input | Faulty Ambient Air Temperature Sensor |
| AAT sensor reporting higher than expected temperature | Damaged or corroded wiring in the sensor circuit |
| Potential issues with climate control and engine performance | Poor electrical connections at the sensor or ECM |
| Possible inaccurate temperature readings on dashboard | Short circuit in the AAT sensor wiring |
| May affect fuel mixture on engine startup | Malfunctioning Engine Control Module (ECM) |
Faulty Ambient Air Temperature Sensor
The Ambient Air Temperature (AAT) sensor is a crucial component in modern vehicles, responsible for measuring the outside air temperature. This information is used by the Engine Control Module (ECM) to adjust various systems, including climate control and engine performance.
Symptoms
- Inaccurate outside temperature readings on the dashboard display
- Climate control system not functioning properly
- Hard engine starts, especially in cold weather
- Illuminated check engine light
Technical Explanation
The AAT sensor is typically a thermistor, which changes its electrical resistance based on temperature. As the temperature increases, the resistance decreases, and vice versa. The ECM interprets this resistance change as a temperature reading. When the P0073 code is set, it means the ECM is detecting a voltage from the sensor that is higher than expected, which translates to an unusually high temperature reading.
Step-by-Step Diagnosis
- Locate the AAT sensor, usually found in the front grille or behind the front bumper.
- Visually inspect the sensor and its wiring for any obvious damage or corrosion.
- Use a digital multimeter to check the sensor’s resistance:
- Disconnect the sensor from the wiring harness.
- Set the multimeter to measure resistance (ohms).
- Connect the multimeter probes to the sensor terminals.
- Compare the reading to the manufacturer’s specifications for the current ambient temperature.
- If possible, use a heat gun or ice pack to change the sensor’s temperature and observe if the resistance changes accordingly.
- If the resistance doesn’t match specifications or doesn’t change with temperature, the sensor is likely faulty.
Solution Methods
- Replace the faulty AAT sensor with a new, OEM-quality part.
- Clear the diagnostic trouble codes (DTCs) using an OBD-II scanner.
- Test drive the vehicle to ensure the problem is resolved and the code doesn’t return.
Cost Estimates
- AAT Sensor: $30 – $150 (varies by vehicle make and model)
- Labor: $50 – $100 (if professional installation is required)
Warnings and Recommendations
Always consult your vehicle’s service manual for the exact location and specifications of the AAT sensor. Incorrect diagnosis or replacement can lead to further issues or damage to the vehicle’s electrical system.
Damaged or Corroded Wiring in the Sensor Circuit
Wiring issues are a common cause of the P0073 code. Over time, exposure to the elements can cause corrosion or physical damage to the wires connecting the AAT sensor to the ECM.
Symptoms
- Intermittent temperature reading fluctuations
- Check engine light coming on and off
- Erratic climate control system behavior
Technical Explanation
The AAT sensor circuit typically consists of two wires: a signal wire and a ground wire. Damage or corrosion can create resistance in the circuit, leading to incorrect voltage readings at the ECM. This can cause the ECM to interpret the signal as a high temperature, triggering the P0073 code.
Step-by-Step Diagnosis
- Visually inspect the entire length of the AAT sensor wiring harness, looking for signs of damage, fraying, or corrosion.
- Check the connector at both the sensor and ECM ends for signs of corrosion or loose pins.
- Perform a continuity test on the wiring:
- Disconnect the sensor and the ECM connector.
- Use a multimeter set to continuity mode.
- Test each wire from the sensor connector to the ECM connector.
- There should be continuity (very low resistance) on each wire.
- Check for shorts to power or ground:
- With the connectors still disconnected, check for continuity between each wire and the vehicle’s chassis ground.
- There should be no continuity. If there is, you’ve found a short to ground.
Solution Methods
- Repair any damaged sections of wiring using proper automotive-grade wire and connections.
- Clean corroded connectors using electrical contact cleaner and a wire brush.
- If damage is extensive, replace the entire wiring harness for the AAT sensor circuit.
- After repairs, clear the DTCs and test drive the vehicle.
Cost Estimates
- Wire repair kit: $10 – $30
- New wiring harness: $50 – $200 (varies by vehicle)
- Professional diagnosis and repair: $100 – $300
Warnings and Recommendations
When working with vehicle electrical systems, always disconnect the battery to prevent short circuits. If you’re not comfortable with electrical repairs, seek professional help to avoid potentially costly mistakes.
Poor Electrical Connections at the Sensor or ECM
Loose or corroded connections can cause intermittent issues and trigger the P0073 code. These problems can occur at either the sensor connector or the ECM connector.
Symptoms
- Flickering or inconsistent temperature display
- Intermittent check engine light
- Climate control system working erratically
Technical Explanation
Poor connections increase resistance in the circuit, which can cause voltage drops or spikes. The ECM interprets these as temperature changes, and if the voltage goes above a certain threshold, it will set the P0073 code.
Step-by-Step Diagnosis
- Inspect the AAT sensor connector:
- Look for signs of corrosion, bent pins, or loose connections.
- Gently wiggle the connector while the engine is running to check for intermittent connections.
- Check the ECM connector:
- Locate the ECM (refer to your vehicle’s manual for the exact location).
- Inspect the main connector for signs of corrosion or damage.
- Ensure the connector is fully seated and locked in place.
- Perform a voltage drop test:
- Connect a multimeter in voltage mode across each connection point.
- With the circuit powered, the voltage drop should be minimal (less than 0.1V).
- A higher voltage drop indicates a poor connection.
Solution Methods
- Clean corroded connections using electrical contact cleaner and a small wire brush.
- Ensure all connectors are fully seated and locked in place.
- If corrosion is severe, replace the affected connectors.
- Apply dielectric grease to connections to prevent future corrosion.
- After repairs, clear the DTCs and verify the fix with a test drive.
Cost Estimates
- Electrical contact cleaner: $5 – $15
- Dielectric grease: $5 – $10
- New connectors (if needed): $10 – $50
- Professional cleaning and repair: $50 – $150
Warnings and Recommendations
Be gentle when cleaning electrical connectors to avoid damaging delicate pins. If you’re unsure about the condition of a connector, consult a professional mechanic.
Short Circuit in the AAT Sensor Wiring
A short circuit in the AAT sensor wiring can cause the ECM to receive an incorrect high voltage signal, triggering the P0073 code.
Symptoms
- Constant high temperature reading
- Check engine light stays on consistently
- Possible issues with other electrical systems
Technical Explanation
A short circuit occurs when the signal wire makes contact with a power source or when the insulation between wires breaks down. This can cause the ECM to receive a constant high voltage, which it interprets as a high temperature, setting the P0073 code.
Step-by-Step Diagnosis
- Perform a visual inspection of the entire AAT sensor wiring harness, looking for any signs of damage or exposed wire.
- Use a multimeter to check for shorts:
- Disconnect the AAT sensor and the ECM connector.
- Set the multimeter to continuity mode.
- Check for continuity between the signal wire and the vehicle’s power sources (battery positive, ignition power, etc.).
- There should be no continuity. If there is, you’ve found a short to power.
- Check for internal shorts in the sensor:
- With the sensor disconnected, check for continuity between its terminals.
- There should be some resistance, but not a direct short (very low resistance).
Solution Methods
- If a short is found in the wiring, repair the damaged section or replace the entire wiring harness.
- If the short is internal to the sensor, replace the AAT sensor.
- After repairs, use heat shrink tubing or electrical tape to protect repaired areas.
- Clear the DTCs and perform a test drive to ensure the problem is resolved.
Cost Estimates
- Wire repair materials: $20 – $50
- New wiring harness: $50 – $200
- New AAT sensor: $30 – $150
- Professional diagnosis and repair: $150 – $400
Warnings and Recommendations
Short circuits can cause damage to other electrical components if left unaddressed. If you’re unable to locate or repair the short, seek professional help immediately to prevent further damage.
Malfunctioning Engine Control Module (ECM)
While less common, a faulty ECM can sometimes be the root cause of a P0073 code. The ECM is responsible for interpreting the signals from the AAT sensor, and if it’s malfunctioning, it may incorrectly process these signals.
Symptoms
- Multiple sensor-related codes present
- Erratic behavior of various vehicle systems
- Persistent check engine light despite replacing the AAT sensor and checking wiring
Technical Explanation
The ECM contains complex circuitry and software that can occasionally fail. If the internal reference voltage or the analog-to-digital converter responsible for reading the AAT sensor signal malfunctions, it can lead to incorrect temperature interpretations and trigger the P0073 code.
Step-by-Step Diagnosis
- Verify that all other potential causes have been ruled out (sensor, wiring, connections).
- Check for software updates for the ECM:
- Consult with a dealer or use a professional-grade scan tool to check for available ECM updates.
- If updates are available, apply them and see if the issue resolves.
- Perform a thorough scan of all vehicle systems:
- Look for other codes or abnormal parameter readings that might indicate a broader ECM issue.
- Test the ECM’s ability to read other sensors:
- Compare readings from multiple sensors to see if they all show abnormal values.
Solution Methods
- If software updates are available, apply them using the appropriate diagnostic tool.
- If the issue persists, the ECM may need to be replaced.
- When replacing the ECM, ensure it is programmed with the correct software version for your specific vehicle.
- After replacement or reprogramming, perform a complete vehicle systems check and test drive.
Cost Estimates
- ECM software update: $50 – $200
- New ECM: $500 – $2000 (varies significantly by vehicle make and model)
- ECM programming: $100 – $300
- Professional diagnosis and replacement: $200 – $500 (in addition to parts cost)
Warnings and Recommendations
Replacing an ECM is a complex procedure that often requires specialized programming equipment. This is typically not a DIY repair and should be performed by a qualified technician or dealership.
In conclusion, the P0073 code, while not immediately critical to vehicle operation, can lead to issues with climate control and potentially affect engine performance if left unaddressed. By following this comprehensive guide, you should be able to diagnose and repair the most common causes of this code. Remember to always start with the simplest and most likely causes, such as checking the sensor and its wiring, before moving on to more complex issues like ECM replacement. If at any point you feel uncomfortable with the diagnosis or repair process, don’t hesitate to seek professional assistance. Regular maintenance and prompt attention to warning lights can help prevent more serious issues down the road.
Frequently Asked Questions About P0073
While aftermarket sensors can work, using an OEM (Original Equipment Manufacturer) part
- Can I still drive my car with a P0073 code?
While the vehicle may still be drivable, it’s best to address the issue promptly. Inaccurate temperature readings can affect climate control and potentially impact engine performance, especially during cold starts. - How often should the Ambient Air Temperature sensor be replaced?
There’s no set replacement interval for AAT sensors. They typically last the lifetime of the vehicle unless damaged by environmental factors or electrical issues. - Will a P0073 code cause my vehicle to fail an emissions test?
In most cases, a P0073 code alone won’t cause an emissions test failure. However, some jurisdictions require all OBD-II monitors to be ready and no codes present to pass the test. - Can extreme weather conditions trigger a false P0073 code?
While extreme temperatures can affect sensor readings, they shouldn’t trigger a P0073 code if the sensor and its circuit are functioning correctly. The code indicates an electrical issue rather than an actual high temperature condition. - How long does it take to diagnose and repair a P0073 code?
Diagnosis typically takes 1-2 hours. Repair time varies depending on the cause, ranging from 30 minutes for a simple sensor replacement to several hours for wiring or ECM issues. - Can a bad battery or alternator cause a P0073 code?
While unlikely, electrical system issues can sometimes cause erratic sensor readings. It’s always a good idea to ensure your vehicle’s charging system is functioning correctly when diagnosing any electrical problem. - Is it necessary to replace the entire wiring harness if there’s a short?
Not always. If the short is localized and easily accessible, repairing the specific section of wiring may be sufficient. However, if the damage is extensive or difficult to access, replacing the entire harness might be more cost-effective in the long run. - Can I use an aftermarket AAT sensor to fix the P0073 code?
While aftermarket sensors can work, using an OEM (Original Equipment Manufacturer) part