OBD-II Trouble Codes

P0171 Code: System Too Lean (Bank 1)

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For combustion engines to function smoothly, it needs to have a mixture of 14.7 parts air to 1 part fuel (14.7:1). To maintain this, the engine control module (ECM) constantly measures the mixture with the help of the oxygen sensor. The ECM has the power to adjust the amount of fuel injected if an increase in the amount of air being fed into the engine is detected. However, when the computer detects incorrect fuel and air ratio, it would trigger the P0171 code.

What Does Code P0171 Mean?

When fuel injection adjustments become too large, the fault code P0171 will be sent to the ECM, which will trigger the check engine light to illuminate. This code could either mean that the oxygen sensor is detecting too much oxygen or too little fuel in the mixture. 

This lack of fuel is known as a lean mixture. In simpler terms, what the code P0171 means is that your system has too lean of a mixture and is not operating optimally.

A vehicle running on a lean mixture causes more pollution because it emits oxides of nitrogen (NOx) that are harmful to the environment. Lean vehicles also have a tendency to misfire as hydrocarbons from unburnt fuel reach the catalytic converters. 

This could cause a spike in the car’s fuel consumption, as well as exhaust damage and emission test failure.

Many owners have reported P0171 for the following makes: Chevrolet (especially on a Chevy Cruze), Ford, Toyota, BMW, and Honda.

Check engine light illuminates possibly for P0171 Code
The check engine light will illuminate when Code P0171 is triggered. The code indicates a lean fuel mixture.

What are the Possible Causes of the P0171 Code?

Lean fuel mixture is a common issue among many vehicles, regardless of the model year. Passenger cars and trucks alike can be affected but it isn’t always triggered by the same failing component. 

For example, a P0171 on your Chevy Cruze could be due to a failing PCV system, while the P0171 on your friend’s Ford F-150 could be from a clogged fuel injector.

Poor fuel mixture is a serious problem that major manufacturers face. If you have a P0171 on your vehicle, for example, the best thing to do is to act as quickly as possible. 

The first step is finding out what’s causing this OBD-II code. Here are some of the possible causes of a P0171 code:

  • Outdated control module software
  • Vacuum leak due to damaged intake manifold gaskets or punctured vacuum and positive crankcase ventilation (PCV) hoses
  • Malfunctioning mass airflow (MAF) sensor
  • Clogged fuel filter
  • Failing fuel pump
  • Clogged fuel injectors
  • Failing fuel pressure regulator
  • PCM issues (e.g., software in need of an update) 
  • Worn-out oxygen sensor

What are the Common Symptoms of the P0171 Code?

Here are the symptoms you need to be aware of that point to a lean mixture problem:

  • Illuminated Check Engine Light
  • Loss of power
  • Misfiring
  • Rough idling
  • Difficulty when starting the car
  • Engine stalling

How to Diagnose the P0171 Code

Since there can be more than one faulty part in the system that’s causing the P0171 trouble code, pinpointing the problem isn’t as straightforward as you would think. 

OBD-II codes, in general, can sometimes indicate severe problems that may require the assistance of a licensed professional. 

For an idea of how to troubleshoot code P0171, check out the video below:

How to Fix the P0171 Code

Fixing a P0171 code depends on which component is triggering the fault. You’ll need to diagnose the code accurately, as outlined above, then perform any necessary repairs. The code could be triggered by anything from a bad sensor to an engine mechanical concern, so you must do your homework.  

Also, keep in mind that all vehicles are different. When troubleshooting and repairing diagnostic trouble codes, you should consult the factory repair information for your application. Repair manuals, such as those from Chilton, are useful, but an ALLDATA subscription is even better. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information.  

Other Notes About the P0171 Trouble Code

Don’t ignore a P0171 code—address it as soon as possible. A poorly running engine due to a lean fuel mixture can fail if left untreated. A small, inexpensive problem could worsen and make your vehicle undrivable.

Instead of shrugging it off, remember that an OBD-II code P0171 is a serious issue that needs your attention. The consequences of ignoring this trouble code include reduced fuel economy, weak performance, poor ride quality—and even engine damage.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

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