The EOBD/OBDII error code P0071 indicates a problem with the Ambient Air Temperature (AAT) sensor’s performance. This sensor, crucial for various vehicle functions, can trigger this code across a range of car manufacturers, including Audi, BMW, Chrysler, Dodge, Ford, Jeep, Mazda, Mitsubishi, and Volkswagen. This article provides a comprehensive guide to understanding, diagnosing, and potentially resolving the P0071 error code.
What Does the P0071 Code Mean?
The AAT sensor measures the outside air temperature and transmits this data as an electrical signal to the Powertrain Control Module (PCM). The PCM utilizes this information to regulate the air conditioning system and display the exterior temperature on the dashboard or overhead console. The PCM cross-references the AAT sensor reading with data from the Intake Air Temperature (IAT) and Engine Coolant Temperature (ECT) sensors. Discrepancies between these readings, particularly after a long cool-down period, can trigger the P0071 code. Furthermore, the PCM continuously monitors these voltage signals to ensure accuracy during engine operation. While electrical issues are the most common culprits, mechanical problems such as incorrect sensor placement or a loose connection can also contribute to this error code.
Recognizing Symptoms of a P0071 Code
Several symptoms may accompany the P0071 code, including:
- Illuminated Malfunction Indicator Lamp (MIL): Also known as the “check engine” light.
- Air Conditioning Malfunction: The AC system might not operate efficiently or at all.
- Inaccurate Temperature Display: The outside temperature displayed on the instrument cluster or overhead console might be incorrect.
Common Causes of the P0071 Error Code
The P0071 code can be attributed to a variety of issues, including:
- Open Circuit: A break in the wiring leading to the AAT sensor.
- Short to Voltage: The signal wire contacting a higher voltage source.
- Short to Ground: The signal wire making unintended contact with the vehicle’s ground.
- Faulty AAT Sensor: The sensor itself may be malfunctioning due to internal damage or wear.
- PCM Failure: Although less common, a faulty PCM can also be responsible.
Troubleshooting and Solutions for the P0071 Code
Before starting any diagnostic procedures, consult your vehicle’s Technical Service Bulletins (TSBs). TSBs often provide manufacturer-recommended solutions for known issues.
1. Visual Inspection:
Locate the AAT sensor, usually positioned near the front of the radiator, behind the grille or bumper. Thoroughly inspect the wiring and connectors for damage, such as fraying, burns, or corrosion. Clean the terminals with electrical contact cleaner and apply dielectric grease.
2. Sensor Testing with a DVOM:
With the ignition off, disconnect the sensor and use a Digital Volt-Ohm Meter (DVOM) to measure its resistance. Compare the reading to the manufacturer’s specifications based on the ambient temperature. Zero ohms or infinite resistance indicates a faulty sensor.
3. Diagnostic Trouble Code (DTC) Scan:
Use an OBDII scanner to clear the error codes and monitor if the P0071 code returns. If not, the issue might have been resolved by addressing connection problems.
4. AAT Sensor and Circuit Testing:
With the ignition off, disconnect the AAT sensor harness. Turn the ignition on and use a scan tool to read the AAT sensor data from the PCM (or relevant module). The reading should be around 5 volts or indicate a very low temperature. With the ignition off, connect a jumper wire across the sensor harness terminals and turn the ignition back on. The reading should now be near 0 volts or indicate a very high temperature. Inconsistencies in these readings point to wiring problems or a potentially faulty PCM.
5. Sensor Replacement: If all other tests prove inconclusive, replacing the AAT sensor is often the necessary solution.
Conclusion
Addressing the EOBD/OBDII error code P0071 involves a systematic diagnostic approach. By understanding the function of the AAT sensor and following the troubleshooting steps outlined in this article, you can effectively pinpoint the root cause of the problem. Remember to consult your vehicle’s specific repair manual and seek professional assistance if needed, especially for tasks like PCM programming or calibration.
