The On-Board Diagnostics (OBD) system uses input from various sensors to monitor the vehicle’s health and performance and to alert the vehicle’s user or potential issues and problems. If the feedback from the sensors does not match the expected values, the vehicle’s computer stores the information on the source and nature of the problem as a trouble code.
The P0071 code is set when the vehicle’s computer detects a potential issue with the ambient air temperature sensor or its circuit. What causes this code and what can you do to fix this issue? This simple guide will answer these questions and more.
What does the P0071 Code Mean?
Diagnostic trouble code (DTC) P0071 stands for “Ambient Air Temperature Sensor Range/Performance.” This code is set when the vehicle’s powertrain control module or PCM detects that the input from the Ambient Air Temperature (AAT) sensor does not correlate with the input of the Intake Air Temperature (IAT) and the Engine Coolant Temperature (ECT) sensors.
The Ambient Air Temperature sensor sends ambient air temperature data as a voltage signal to the PCM. In some vehicles, the PCM uses this information to regulate the air conditioning system and to display the outside air temperature.
The PCM compares data from the AAT sensor with the data gathered from two other sensors: the Intake Air Temperature (IAT) sensor and the Engine Coolant Temperature (ECT) sensor. The PCM compares these readings when the ignition switch is first turned on after a long soak or cool-down period. The PCM also monitors the voltage signals from these sensors when the engine is fully warmed up.
The caveat is that while the PCM keeps track of the Ambient Air Sensor on some vehicles, it’s related to vehicle climate control rather than engine control.
P0071 comes from a family of codes, all pointing to issues with the Ambient Air Temp Sensor:
- P0071, Sensor Circuit Performance
- P0072 Sensor circuit low
- P0073 Sensor circuit high
- P0074 Sensor circuit erratic
Note: The definition of code P0071 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.
What are the Possible Causes of the P0071 Code?
As mentioned above, diagnostic trouble codes indicate the nature and source of the problem, not the specific issue. Many factors can come into play when a single trouble code sets.
Determining the main reason why the P0071 code registers is very important to understand the underlying issue better and to establish an effective, long-term fix. Listed below are some of the most common problems behind P0071:
- Ambient air temperature sensor failure
Wiring issues, such as:
- AAT Signal Circuit high resistance
- AAT Signal Circuit shorted to ground
- AAT Signal Circuit shorted to the sensor ground circuit
- AAT Signal Circuit shorted to voltage
- Sensor ground high resistance
- PCM failure (rare)
What are the Common Symptoms of the P0071 Code?
When information from the sensors falls out of the expected range, the vehicle’s computer saves the information as a DTC. When these trouble codes are saved, the vehicle’s computer sends a signal that illuminates the appropriate indicator lights.
Aside from illuminated indicator lights, other signs can manifest when you’re dealing with many DTCs. Below are just some of the most common symptoms that you may notice with P0071:
- Malfunction indicator light or check engine light on
- Air conditioning may not perform properly
- Instrument cluster may not read outside temperature accurately
- Overhead console may not read outside temperature accurately
How to Diagnose the P0071 Code
Richard McCuistian, ASE Certified Master Automobile Technician: Technicians use a similar strategy, and you can too. If your scan tool gives live data, just pull up the ECT, IAT, and TOT PIDS (Engine Coolant, Intake Air, and Transmission Oil Temps) and compare them with each other after the vehicle has been sitting for three or four hours and make sure they all agree within a degree or two. If a sensor doesn’t agree with the other two, it bears investigation. If, however, the vehicle is in a garage and there’s an infrared heater baking the hood with heat, that needs to be factored in as well.
Diagnosis can be quite difficult for P0071 because there are a lot of reasons why it can register. In order to formulate a solution to the problem, the very root cause must first be determined. A thorough analysis of the issue and an accurate diagnosis are important to address trouble codes such as the P0071 code.
Repair manuals and databases are excellent sources of accurate information and detailed repair procedures. They also contain various diagrams and illustrations that help you visualize and understand certain topics better. Consulting repair manuals also help you save time and money.
Below is a helpful video resource if you want to learn more about the P0071 code:
How to Fix the P0071 Code
There are other factors that can complicate your troubleshooting process, aside from the fact that there are multiple possible causes behind trouble codes. Manufacturers make vehicles differently so components and configurations vary.
There is no single way of addressing trouble codes that would apply for every vehicle. Repair instructions to address P0071 in Dodge Caravans may not necessarily be the same as the repair procedures for fixing P0071 in Mercedes-Benz vehicles.
Repair manuals and databases can help experienced DIYers because they contain specific instructions and detailed information for OBD-II repairs. However, the information in these sources may be too technical for a beginner. If you don’t know what to do to address the P0071 code, you should have your vehicle fixed by a certified mechanic and/or technician.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.