P0171 Code: Symptoms, Causes, and How to Fix

Published: March 30, 2022

Fuel and air must be mixed correctly for your engine to run efficiently. You won't be able to get your combustion engine to work efficiently or effectively if there is too much or too little fuel.

Your vehicle will store a P0171 code if it detects excessive air entering the chambers. This increase in oxygen can be caused by several factors, including a faulty sensor or a malfunctioning fuel pump.

Your car needs to be diagnosed as quickly as possible if you want to prevent severe damage. Learn more about diagnosing the cause of code P0171, what it means for your vehicle, and how to fix it by reading on.

What Does Code P0171 Mean?

Your engine block is not receiving a good air-fuel ratio when you get a P0171 code. The main cause of this code is usually one of two things. Either too much air is present in the lines, or there is not enough fuel.

There are often vacuum leaks that allow an excess of oxygen into the line when there is too much air in the line. A lack of fuel may also prevent an adequate air supply from reaching the engine.

It is possible that a faulty fuel injector or fuel pump could be to blame for the second scenario. Regardless of the root cause, a lean engine has a high air to gasoline ratio. When the engine runs rich, it has too much fuel.

Symptoms of Code P0171

Occasionally, you won't notice any difference in how your vehicle operates when your check engine light comes on if the light is associated with a P0171 code (after troubleshooting).

You cannot run your engine properly if there is too much air inside. You might hear a rough idle or a coughing sound from your engine when it's running, but you aren't driving.

When you accelerate or drive uphill, your car may feel like it lacks power. It might even misfire when you accelerate.

Having a code P0171 does not necessarily mean that your car is driving differently. It could be a faulty sensor. These parts do fail over time.

However, you still need to make sure the parts around the sensor are working, even if there aren't any other symptoms. There's no point in replacing expensive parts without any reason.

Causes of Code P0171

When you see the code P0171 in your vehicle, the first thing to check is the vacuum system. Extra air may enter the vacuum system when the vacuum line is torn or cracked. The PCV hose, vacuum, or intake manifold gasket can leak, causing diagnostic trouble code P0171.

If all the vacuum lines are solid, the source is likely inside the fuel system. In the case of a failing or weak fuel pump, the engine won't receive enough gasoline. Similarly, dirty fuel filters or clogged fuel injectors can cause a backup.

It remains possible to find the cause of your check engine light. Even if your vacuum system is leak-free, there is plenty of gas entering the engine, and the code P0171 is still shown.

You might have a dirty oxygen sensor, a damaged mass air flow sensor, or a faulty air-fuel ratio sensor. There is also the possibility of an exhaust leak influencing the readings.

Is Code P0171 Serious?

It is important to take the reading from the check engine light seriously whenever it is on. There is no exception to this rule when it comes to P0171. When this code is stored in the engine, your vehicle should not be driven far, if at all.

A lean engine cannot run efficiently because there is not enough gasoline. This can lead to the vehicle not being able to accelerate fast enough to meet traffic speeds or to climb steep hills. In addition, the car may become overheated and irreparable.

P0171 codes are more likely to appear in turbocharged vehicles whose boost has been increased. If you add more air, you will produce more power, but you will need more fuel to maintain that ratio.

The most likely cause of code P0171 is that your vehicle is not using its fuel efficiently. Every time you drive, you'll waste money and gas.

How to Fix

A P0171 code can be cleared by following straightforward diagnostic and repair steps. You're sure to find the problem if you follow the steps correctly. You must first clear all other codes before proceeding. Now you can resolve the problem.

Make sure the vacuum system is leak-free first. Use a vacuum pressure gauge if you hear any strange hissing sounds around the engine.

Make sure that enough gasoline gets into the engine using a fuel pressure gauge. During this step, you should look at the fuel filter and injectors.

To determine your oxygen sensors' health and functionality, you should run diagnostic tests if there are no other problems.

Are you interested in learning more about cars and their maintenance? Head over to the KeepDriving website and check out our blog post on what causes black smoke from the car’s exhaust.

Founder, Editor-in-Chief Carmelo Pickel is the Founder and Editor-in-Chief of Keep Driving, with almost 20 years of experience working in the industry. Before founding Keep Driving, Carmelo held leadership roles for over a decade on top automotive dealership corporations across North America, handling various leadership roles in Sales, Marketing, and Incentives.
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