P0171: System Too Lean Bank 1

When you receive the diagnostic trouble code P0171, you likely have an issue in your exhaust system. If that’s the case, you need to find out how do I fix trouble code P0171? Learn more about your air/fuel ratio and some common symptoms, causes and solutions for this error code.

Check Your Check Engine Light

What Does P0171 Mean?

Code P0171 is triggered by the bank one oxygen sensor. It alerts your system when the condition is too lean, or there’s too much oxygen in the exhaust. So, what does the code P0171 mean? The symptoms and causes will help you determine the exact issue and how to fix it.

Your bank one oxygen sensor is the first downstream sensor. It verifies the correct air/fuel ratio leaving the cylinders of your vehicle’s engine. The optimal ratio is 14.7:1. When your powertrain/engine control module receives a reading that indicates there’s too much oxygen and the ratio is incorrect, it sends an error code P0171.

Symptoms of a P0171

For most trouble code P0171 situations, you won’t notice any performance issue. However, some lean situations cause your vehicle to have these performance problems:

  • Surging or hesitating acceleration
  • Spark knock or detonation
  • Reduced power
  • Rough idle

More commonly, you’ll only be alerted by the presence of a lit CEL. Look for one of these common causes to determine how to solve the problem code.

Fortunately, many of these issues are simply caused by faulty sensors. A true leak should be repaired immediately, so it’s still essential that you find the cause and restore your sensors. Dirty or damaged sensors can often be the only issue with your air/fuel ratio.

Common Causes

There are many minor or major repairs that could create this issue. Start with the easiest issues and work your way through to identify the cause of your problem code. A common problem is a dirty mass air flow, or MAF, sensor. Oil and other contaminants can cause this sensor to give a false reading and produce the error code.

Next, check the entire vacuum and PCV hoses for any leaks. These are the most common causes and also some of the easiest to fix. Less common issues include a dirty fuel filter, low fuel pressure or a leaking intake manifold gasket.

Solutions and Repairs

Your first step should be to review your service manual and find the location of your MAF sensor. It’s very likely that your sensor is simply dirty and sending out a false signal. This is particularly true if you use oiled air filters that have too much oil on them, causing contaminants to cling to your MAF sensor. Once you find your sensor, inspect it for any silicone potting material damage. Silicone protects the circuitry of your sensor and can leak, causing damage to your sensor’s circuitry.

Once the sensor is cleaned and working properly, your next step should be to check the vacuum of the system. Consider investing in a smoke machine or have a professional use a machine to check for any vacuum leaks. Replacing the pipe or hose area with a leak is another common solution. Exhaust leaks are common between the engine and first oxygen sensor.

For more unusual issues, you’ll need to replace your bank one oxygen sensor, PCV valve, fuel injector, or fuel filter. Damage to these parts can also cause your OBD-II scanner error code P0171 problem. Once you find the solution and repair or replace the appropriate part, check your vacuum and reset your trouble code to test whether you’ve fixed the issue or need to look for further vacuum leaks.

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