The OBDII error code P0073 indicates a “Ambient Air Temperature Sensor Circuit High” issue. This diagnostic trouble code is generic and applies to vehicles equipped with OBDII systems. However, it is more commonly observed in vehicles from manufacturers like Audi, BMW, Chrysler, Dodge, Ford, Jeep, Mazda, Mitsubishi, and VW.
Understanding the P0073 Code: Ambient Air Temperature Sensor Circuit High
The Ambient Air Temperature (AAT) sensor plays a crucial role in your vehicle’s engine management system. It measures the outside air temperature and converts this reading into an electrical signal. This signal is then sent to the Powertrain Control Module (PCM), also sometimes referred to as the Engine Control Module (ECM). The PCM uses this information for several functions, primarily to optimize the air conditioning system’s performance and to display the accurate outside temperature on your dashboard or overhead console.
The PCM doesn’t rely solely on the AAT sensor. It also monitors other temperature sensors within your vehicle, such as the Intake Air Temperature (IAT) sensor and the Engine Coolant Temperature (ECT) sensor. Upon starting your car after a significant cool-down period, the PCM compares the readings from the AAT sensor with those from the IAT and ECT sensors. Ideally, these readings should be relatively close when the vehicle is cold. Similarly, when the engine reaches its operating temperature, the PCM checks if the sensor signals are within expected parameters.
The P0073 code is triggered when the PCM detects a voltage signal from the AAT sensor circuit that is abnormally high. This “circuit high” condition often points to electrical circuit problems rather than a sensor malfunction itself. It signals that the voltage in the AAT sensor circuit is exceeding the normal operating range, indicating a potential fault in the wiring or the sensor.
Common Symptoms of a P0073 Error Code
When your vehicle logs a P0073 code, you may experience several noticeable symptoms:
- Malfunction Indicator Light (MIL) or Check Engine Light is illuminated: This is the most immediate sign that something is amiss with your vehicle’s system. The light will appear on your dashboard to alert you to a detected issue.
- Air Conditioning System Malfunctions: The A/C may not cool as effectively as it should, or it might not operate at all. The PCM uses AAT sensor data to optimize A/C performance, and inaccurate readings can disrupt this process.
- Inaccurate Outside Temperature Readings: The temperature displayed on your instrument cluster or overhead console might be incorrect. It could show excessively high or consistently wrong temperature values.
- Overhead Console Temperature Display Issues: Similar to the instrument cluster, the temperature display in the overhead console might also be inaccurate or non-functional.
Potential Causes of the P0073 Code
Several factors can lead to a P0073 trouble code. Pinpointing the exact cause is essential for effective repair. The most common culprits include:
- Open Circuit in the AAT Sensor Signal Wire: This means there’s a break or disconnection in the wire that carries the signal from the AAT sensor to the PCM. This interruption prevents the signal from reaching the PCM correctly, resulting in a “circuit high” reading as the PCM detects an unexpected voltage level.
- Short to Voltage in the AAT Sensor Signal Wire: A short to voltage occurs when the signal wire comes into contact with a voltage source, such as the positive side of the vehicle’s electrical system. This causes excessive voltage in the circuit, which the PCM interprets as a “circuit high” fault.
- Faulty Ambient Air Temperature Sensor: While less frequent than wiring issues, the AAT sensor itself can fail. If the sensor malfunctions internally, it might send an incorrect, high voltage signal to the PCM.
- PCM Failure (Unlikely): In rare cases, a faulty PCM could misinterpret sensor signals or incorrectly trigger the P0073 code. However, PCM failure is usually the last thing to suspect and should only be considered after ruling out all other possibilities.
Diagnosing and Resolving the P0073 Error Code
Troubleshooting a P0073 code systematically is crucial to identify and fix the root cause efficiently. Here’s a step-by-step approach:
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Check for Technical Service Bulletins (TSBs): Before diving into complex diagnostics, always check for TSBs issued by your vehicle manufacturer. TSBs can provide valuable information about known issues and common fixes related to the P0073 code for your specific make and model. This can save significant time and effort.
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Locate and Inspect the AAT Sensor: The AAT sensor is typically located at the front of the vehicle to accurately measure ambient air temperature. Common locations include:
- Behind the front grille
- In front of the radiator
- Near the front bumper area
Once located, visually inspect the sensor, its wiring, and connectors. Look for:
- Physical damage: Cracks, breaks, or any signs of impact.
- Wiring issues: Scraping, rubbing, bare wires, or wires that are stretched or broken.
- Connector problems: Loose connectors, corrosion, bent or damaged pins, or signs of melting.
Alt text: Visual inspection of the Ambient Air Temperature Sensor connector and wiring harness for signs of damage like corrosion or frayed wires, crucial step in P0073 code diagnosis.
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Clean Connectors: Disconnect the AAT sensor connector and carefully inspect the terminals (metal pins) inside both halves of the connector. Look for:
- Corrosion: A green or white powdery substance indicates corrosion.
- Burn marks: Signs of overheating or electrical arcing.
If corrosion is present, use an electrical contact cleaner and a plastic bristle brush to gently clean the terminals. Allow the cleaner to dry completely and apply dielectric grease to the terminals before reconnecting the connector. Dielectric grease helps prevent future corrosion and ensures a good electrical connection.
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Sensor Resistance Test: Use a Digital Volt-Ohm Meter (DVOM) to test the AAT sensor’s resistance.
- Disconnect the AAT sensor connector.
- Set your DVOM to measure resistance (Ohms – Ω).
- Connect the DVOM leads to the two terminals on the AAT sensor itself (not the wiring harness connector).
- Compare the measured resistance value with the expected resistance range specified in your vehicle’s repair manual or a reliable online resource. The resistance value of the AAT sensor is temperature-dependent; lower temperatures should correspond to higher resistance, and vice versa.
- If the DVOM reads 0 Ohms or infinite resistance (often displayed as “OL”), the sensor is likely faulty and needs replacement.
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Circuit Voltage Test: Check for proper voltage supply to the AAT sensor circuit.
- Disconnect the AAT sensor connector at the sensor.
- Turn the ignition key to the “ON” position (engine off).
- Use your DVOM to measure voltage between one of the terminals in the wiring harness connector (the connector that normally plugs into the sensor) and a known good ground (like the vehicle’s chassis).
- You should typically read around 5 volts. This voltage is supplied by the PCM to the sensor.
- If you don’t read 5 volts, there might be a problem with the wiring between the PCM and the sensor, or potentially a PCM issue (less likely).
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Scan Tool Data Monitoring: If you have access to a scan tool, use it to monitor the AAT sensor readings in real-time.
- Connect the scan tool to your vehicle’s OBDII port.
- Navigate to the live data or sensor data section.
- Locate the Ambient Air Temperature sensor reading.
- Observe the reading with the sensor connected and disconnected.
- With the sensor connected, the reading should reflect the approximate ambient temperature.
- If the reading is consistently very high or very low, or doesn’t change, it indicates a potential sensor or circuit problem.
- You can also try clearing the P0073 code with the scan tool after addressing any connection issues. See if the code returns. If it doesn’t, the problem might have been a loose or corroded connection.
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Wiring Harness Inspection and Repair: If the voltage tests indicate a wiring problem, carefully inspect the wiring harness between the AAT sensor and the PCM. Look for:
- Continuity issues: Use a DVOM to check for continuity (a complete, unbroken circuit) in each wire of the AAT sensor circuit.
- Shorts to voltage or ground: Check for shorts by testing for unwanted voltage or ground on the signal wire.
- Repair any identified wiring faults: This might involve repairing broken wires, replacing damaged sections of wiring, or fixing shorts.
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PCM Testing (Advanced): If all other tests pass and the P0073 code persists, a PCM issue is a remote possibility. PCM testing often requires specialized equipment and expertise. If you suspect a PCM problem, it’s best to consult a qualified automotive technician.
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Professional Diagnosis: If you are uncomfortable performing these diagnostic steps or the problem persists, it’s advisable to seek assistance from a trained automotive diagnostician. They have specialized tools and knowledge to accurately diagnose and repair complex automotive electrical issues.
Important Note: PCMs are complex components and sometimes require programming or calibration after replacement. Always consult your vehicle’s service information and follow manufacturer-recommended procedures when dealing with PCM-related issues.
By following these troubleshooting steps, you can effectively diagnose and resolve the P0073 “Ambient Air Temperature Sensor Circuit High” error code, restoring your vehicle’s A/C system functionality and ensuring accurate temperature readings. Remember to prioritize safety and consult a professional if you encounter any difficulties.
