P0171: System Too Lean Bank 1

The internal combustion engine needs the proper amount of air and fuel mixed together in order to have successful combustion. If there is too much air or too much fuel, then it can diminish the performance of the engine after the mixture is ignited. Then you could experience poor engine power and weak acceleration as you apply your foot to the gas pedal.

In a normal combustion situation, the internal combustion chamber will have 14.7 parts air and 1 part fuel. Once this mixture is ignited, your engine will function normally and produce the power you need behind the wheel. But if your combustion chamber ever has over 14.7 parts air with only 1 part fuel, then you have what is called a lean air-to-fuel ratio.

The first two symptoms of this problem will be your Check Engine light illuminating on the dashboard and a lack of engine power. This will be followed by a rough idle, engine misfiring, and engine coughing. Any of these symptoms should prompt you to take your vehicle to an auto technician and have them run a diagnostic check on the engine control unit.

If you have a lean air-to-fuel ratio, then diagnostic code P0171 will appear on the display screen. The official definition of P0171 is “System Too Leak Bank 1,” which means you have more air than fuel in your combustion chamber. There are several possible reasons for this problem. You could have a bad fuel pump, vacuum leaks, bad mass airflow sensor, clogged fuel filter, clogged fuel injectors, leaky exhaust, bad oxygen sensor, or bad air-to-fuel ratio sensor.

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It is not that expensive to replace bad sensors. The costliest replacements would be your fuel pump, vacuum, fuel filter, and fuel injector. In any event, your job is to figure out which component is causing P0171 to occur. It is common for amateurs to make mistakes when checking for the cause of this problem. They’ll just assume the air-to-fuel sensor or the oxygen sensor is the reason for the problem. But you must consider the other possible causes too.

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