Code P0171 (Symptoms, Causes and How)

Your engine needs the correct ratio of fuel and air to run efficiently. If there is too much or too little, your combustion engine will not work as well or as efficiently as it should.

When too much air enters the chambers, your vehicle will store the P0171 code. This increase in oxygen can be caused by a variety of problems, from a faulty sensor to a problem with the fuel pump or vacuum system.

It is essential to find the root cause quickly before your car suffers serious damage. Read on to learn more about how to diagnose the cause of the P0171 code, understand how it may affect your vehicle, and fix the problem.

What does the P0171 code mean?

A P0171 code indicates that the air-fuel ratio entering your engine block is not ideal. This code usually causes two main problems. There is too much air or not enough fuel in the lines to create the correct ratio.

When there is too much air, you will often find a vacuum leak that allows excess oxygen to enter the line. Alternatively, the engine may not be receiving enough fuel to balance the standard amount of air.

 

The second case may indicate a problem with your fuel pump or faulty fuel injectors.

Regardless of the underlying cause, a situation with a higher air-to-fuel ratio is called a lean engine. If there was too much fuel, the engine would run rich.

Related: Code P0174 (System Too Thin, Bank 2)

Code P0171 Symptoms

Sometimes, when your check engine light comes on, you won’t notice any difference in how your vehicle runs. When the light is accompanied by a P0171 code (after scanning for trouble codes), there will be other symptoms.

When there is too much air inside, your engine cannot run properly. When your engine is running, but you are not driving, you may notice an Idle Riddle or a coughing engine.

While driving, your car may seem to lack power. when accelerating or driving uphill. You could even hear or feel the hum of your engine.

If you don’t notice your car driving differently when it displays a P0171 code, your sensor may be faulty. These parts fail.

However, even if there are no other symptoms, you should confirm that the parts around the sensor are working. You don’t want to replace an expensive part for any reason.

Causes of Code P0171

The vacuum system is the first area to check when your vehicle registers a P0171 code. A small tear or crack in the vacuum lines introduces additional air into the system. A leak causing the P0171 diagnostic trouble code can occur anywhere in the engine intake, including the PCV hoses, vacuum hoses, and intake manifold gasket.

If all vacuum lines are solid, the fuel system is probably the source. A weak or faulty fuel pump will not push enough gasoline to the engine. Clogged fuel injectors or a dirty fuel filter will cause similar blowback.

In cases where the vacuum system is not leaking, the engine is receiving enough gas, and the P0171 code is still displayed with the check engine light, there is still hope of finding the cause.

The oxygen sensor, mass air flow sensor, or air-fuel ratio sensor may be dirty, faulty, or damaged. Alternatively, there could be an exhaust leak that would affect the readings.

See also: 7 Places to Look for Vacuum Leaks

Is code P0171 serious?

Any time your check engine light comes on, you should take the reading seriously. The P0171 code is no exception to this rule. When the engine stores this code, you should not drive your vehicle much, if at all.

When your engine is running low, there is not enough gasoline for it to run efficiently. As a result, there is a risk that the vehicle will not be able to accelerate to keep up with traffic speeds or to climb a steep grade. The car could also overheat and become beyond repair.

Those who modify their turbocharged vehicle by increasing boost are more likely to get a P0171 code. More air generally equals more power, but you must add more fuel to keep the ratio in line.

At best, when your vehicle displays the P0171 code, it is not using its fuel efficiently. You will waste gas and money every time you drive.

How to fix

There are some simple diagnostic and repair steps to clear a P0171 code. If you follow the steps in the correct order, you will surely find the problem. First, erase all other codes on your car. Then you can start working on it.

First, check the vacuum system for leaks. You can use a vacuum gauge or listen around the engine for unusual whistling sounds.

Next, use a fuel pressure gauge to make sure there is enough gasoline in the engine. Also, check the fuel filters and injectors during this step.

If there are no other issues, your final step is to run diagnostic tests to determine the health and functionality of your oxygen sensors.