OBD2 Code P0171: What It Means

Figuring out why your Check Engine Light is on means deciphering OBD-II (or “OBD2”) codes, and that can be kind … Continued

Figuring out why your Check Engine Light is on means deciphering OBD-II (or “OBD2”) codes, and that can be kind of annoying. That’s why Car Bibles did it for you! You’re welcome, now let’s get into solving your issue.

OBD2 P0171: What It Means

The code reads as “system too lean (bank 1),” meaning that your engine is getting too much air and not enough fuel on the first bank of cylinders. For most cars, this will be the only bank. This code can range from engine-destroying madness to completely harmless depending on your car. Either way, this is not a code you should ignore.

Likely Symptoms 

Here’s what you may experience due to the P0171 code:

  • Loss of power and acceleration.
  • The engine is not running optimally, so it may go into a low-power limp-home mode.
  • Engine misfire, hesitation, rough idle.
  • Engine won’t run well in any rpm range if the problem is large enough.
  • Engine won’t start.
  • Vacuum leak or intake leak causing lean code mean the engine can’t read airflow correctly.
  • Bad fuel economy.
  • Engine attempts to save itself with a limp-mode.

Probable Causes

Here’s what could be causing the issue:

  • Vacuum leak.
  • There could be a leak somewhere in your air intake system causing extra air to enter the engine, or a leak in a vacuum hose causing the engine computer to have incorrect readings.
  • Dirty or malfunctioning Mass Air Flow sensor. The MAF is responsible for reading air entering the engine, if it does not function properly, it will cause a lean or rich condition.This would be a common cause of the P0171 code.
  • Fuel injector, fuel pump, or fuel pressure regulator failing.
  • In the rarest cases, the fuel system experiences a failure and isn’t able to deliver the fuel needed, though it is usually accompanied by another code if that is the case.

What Part Is Potentially Affected?

Most commonly, this code is caused by a faulty and/or dirty Mass Air Flow Sensor (MAF) or a simple vacuum leak caused by a torn intake hose after the MAF. Give the intake system a good visual inspection, and physically move it to expose any cracks that have formed. 

Possible Fixes

Here are the most common fixes to remedy the P0171 code:

  • Clean or replace the mass air flow sensor (MAF).
  • Remove the MAF from the vehicle and spray it with MAF cleaner, available at any auto parts store. Usually, its two screws and a connector, simple repair.
  • Repair or replace the intake hoses if there is evidence of tearing.
  • Remove the intake hose by unscrewing some clamps, find any potential tears, and install a new one if any tears are found.
  • On turbocharged cars, inspect all piping from the intake, to the turbo, to the intercooler, to the intake manifold and find any loose clamps or tears.
  • If there are any loose clamps, tighten them up. If there are torn hoses, replace immediately.

Finding The Parts You Need

Now that you’ve figured out what’s wrong with your hooptie, let’s talk about where you’re gonna find that part’s replacement.

There are plenty of places you can buy auto parts from, but Car Bibles gets paid if you click this Advance Auto link so that’s the one we’re serving up. Advance Auto Parts also has delivery, curbside pickup, and a host of helpful diagrams to aid your repair!

Chris Rosales

Chris RosalesChris has owned 12 cars of questionable quality, is an experienced motorsports photographer, and a good all-around wrench. When he isn’t tinkering with his car in his home garage, you can catch Chris in the canyons around SoCal. He also hopelessly hankers for Euros, but he honestly knows he should get something Japanese, eventually. Contact the author here.