Subaru P0171 Code: Symptoms And Its Causes [Issue Fixed]

Illumination of the p0171 code, which indicates “System too lean (Bnak1), is commonly reported by Subaru vehicle owners. Have you also encountered the code on the dashboard of your Subaru Forester, crosstalk, Outback, Impreza, WRX, or any other model you own? There is no need to worry because you can easily fix the Subaru p0171 code by following some basic mechanical tasks.

In this guide, I will assist you in understanding what the p0171 Subaru code means and why it occurs, the common causes behind the error, symptoms that point towards the main root of the problem, and how you can easily fix the issue.

Understanding the Subaru P0171 Code

The p0171 code indicates that the engine fuel system is running in lean condition, which means that due to too much air and not enough fuel, a lean mixture is produced, which can disrupt the functioning of the engine and cause several issues, such as rough idle, decreased fuel efficiency, and reduced engine performance, 

A balanced air-fuel ratio is crucial for the engine to work efficiently. When it becomes imbalanced, the engine control module (ECM), which continuously monitors the ratio, will trigger a warning code p0171 on the dashboard to inform the owner about the rising issues in the engine bank1.

Symptoms of the P0171 Code in a Subaru

If you’ve experienced the blinking of code, then you may experience the following symptoms, which ensure the occurrence of issues in the engine’s intake system.

• Check engine light: The first and most common sign you observe indicates that the check engine light containing the diagnostic trouble code p0171 will start flashing on the screen.
• Rough idle: The engine will begin reacting roughly or shaky due to insufficient fuel and lean mixture conditions.
• Decreased fuel efficiency: The lean mixture can cause increased fuel consumption, which you might notice when refueling fuel more times than before the code illumination.
• Lack of power: You will experience poor acceleration while driving the vehicle.

Common Causes of the Subaru P0171 Code

Knowing the common culprits is crucial to diagnosing and fixing the malfunctioning component and triggering the p0171 code.

Vacuum Leaks

When vacuum leaks occur in any intake system components, such as manifold gaskets and vacuum hoses, the unmetered air can enter the engine, leading to a lean air-fuel mixture. 

Mass airflow sensor (MAF) Issues

When the mass air flow sensor becomes dirty or clogged, it fails to measure the engine’s air entering. Due to a bad MAF sensor, excessive air might enter the engine and cause a lean condition.

Oxygen sensor problems

Over time, oxygen sensors become faulty or start malfunctioning and need replacement. A faulty O2 sensor might send incorrect readings to ECM, which might cause the computer to show the p0171 code on the dashboard.

Weak fuel pump

A weak fuel pump will fail to deliver the right amount of fuel required for the fuel system to provide power to the engine. A clogged or dirty fuel filter can disrupt the airflow, leading to more air and less fuel in the combustion chamber.

Clogged fuel injectors

Over time, fuel injectors become dirty and need cleaning or replacement if they fail to function. A clogged fuel injector can disrupt the fuel injection into the engine’s internal consumption chamber, where it’s mixed with air. 

How to Fix the P0171 Code Subaru

Here’s the step-by-step guide to potential solutions to help you resolve the Subaru code p0171.

Check for Vacuum Leaks

• Visual inspection: Inspect intake system components and look for any signs of vacuum leaks. Especially take a look at the hoses, manifold gaskets, seals around the intake manifold, and throttle body. Check the connections and ensure no cracks, signs of wear, or damage.
• Smoke test: Some leaks are very hard to detect with visual inspection, and a smoke test helps to find hard-to-spot leaks. 

Mass airflow sensor inspection

• MAF sensor cleaning: Dirt and debris can cause the sensor to deliver incorrect readings. Clean the sensor with a high-quality cleaner to remove accumulated dirt & debris, and then reinstall it.
• MAF sensor replacement: If cleaning doesn’t resolve the p0171 dtc fault code and it’s still blinking on the dashboard, then you must replace the old one and install a new

Oxygen sensor checking

• Test the O2 sensor: While diagnosing the issue, test the O2 sensor with a multimeter or error code scanner tool like OBD-II to get data, which helps to know whether the sensor is faulty.
• O2 sensor replacement: If the sensor is defective or sends incorrect data to ECM, then the replacement of the O2 sensor should be done promptly.

Exhaust system inspection

• Check for exhaust leaks: Leaks near the oxygen sensor can influence the sensor readings and cause the engine to think unmetered oxygen is entering the engine, which results in the illumination of the p0171 Subaru code.

Inspection of fuel injectors

• Cleaning: Professionally clean the fuel injectors if they are found to be clogged or dirty.
• Replacement: If cleaning doesn’t work and fuel injectors fail to deliver fuel to the engine, you might need to replace them.

Car Brands Commonly Affected by P0171 Code

Here’s the breakdown of top car brands in which the p0171 dtc code is also experienced by the owners.

In A Nutshell

Triggering of the Subaru p0171 code is common among many owners, but it’s crucial to fix the error before it raises severe potential problems. After understanding the symptoms, causes, and solutions to resolve the issue, you can prevent your vehicle from critical damage and save time & extra cost in fixing further issues. 

However, try to follow the easy tasks such as fuel filter replacement and vacuum leak checking because it can be without advanced equipment and professional knowledge. Suppose you’re struggling and facing difficulties in resolving the p0171 code Subaru. In that case, it’s recommended that you consult an expert mechanic to diagnose and fix the problems that are to be diagnosed and repaired.

Frequently Asked Questions

What does the Subaru P0171 code mean?

The Subaru DTC code P0171 indicates a “System Too Lean (Bank 1),” meaning the engine’s air-fuel mixture has too much air and insufficient fuel on the side of the engine bank1.

What are the common symptoms of a P0171 code on a Subaru?

Common symptoms include:

• The Check Engine Light.
• Rough idling.
• Increased fuel consumption.
• Lack of power.
• Stalling.
• Potential engine damage.

Can I drive my Subaru with a P0171 code?

While driving with a P0171 code is possible, it’s not recommended for long periods. Continuing to drive can lead to engine performance issues and critical damage if left unresolved for a long period.