Technical Description
The engine is running too lean on Bank 1.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to all makes and models of vehicles (1996-newer). However, the specific repair steps may vary slightly depending on the model. This engine code article is applicable to Toyota, Chevrolet, Ford, Nissan, Honda, GMC, Dodge, etc.
In simple terms, this code indicates that the oxygen sensor in Bank 1 has detected a lean condition, meaning there is too much oxygen in the exhaust. On V6/V8/V10 engines, Bank 1 refers to the side of the engine that has cylinder #1. The P0171 code is one of the more common trouble codes.
This code is triggered by the first downstream (front) O2 sensor. The sensor measures the air:fuel ratio leaving the engine’s cylinders, and the vehicle’s powertrain/engine control module (PCM/ECM) uses that reading to adjust and maintain the engine running at the optimal ratio of 14.7:1. If there is an issue and the PCM cannot maintain the 14.7:1 ratio, and instead there is too much air, this code is triggered.
It is recommended to also read our article on short and long term fuel trims to gain a better understanding of the engine’s operation. Note: This DTC is very similar to P0174, and your vehicle may display both codes simultaneously.
Symptoms
You will most likely not notice any drivability problems, although there may be symptoms such as:
Causes
A code P0171 may indicate that one or more of the following has occurred:
Note: The use of “oiled” air filters may cause the MAF to become dirty if the filter is over-oiled. Some vehicles also have an issue where the MAF sensors leak the silicone potting material used to protect the circuitry.
Possible Solutions
Many times, cleaning the MAF sensor and identifying/fixing vacuum leaks can resolve the problem. If you have a limited budget, start with these steps, but keep in mind that they may not be the definitive solution. Possible solutions include:
