P0171 OBD-II System Too Lean (Bank 1) Trouble Code

P0171 is a diagnostic trouble code that stands for System Too Lean (Bank 1). It indicates that there is very little fuel or too much air in the first bank of the engine (Bank 1).

In this article, I will be talking about P0171, its symptoms, how to fix it, and how much it costs to fix the problem.

What Does The P0171 Trouble Code Mean?

P0171 OBD-II System Too Lean (Bank 1) Trouble Code

The P0171 trouble code stands for System Too Lean (Bank 1) which means that the vehicle’s computer has detected insufficient fuel flow or increased oxygen flow in the first bank of the engine and both scenarios lead to ”lean condition”. A lean condition is when the engine gets very little fuel or too much air.

In order for the combustion to occur, the engine requires a pre-calculated amount of fuel and air. If the fuelOpens in a new tab.

Which Models Are Affected By The P0171 Trouble Code

MakeAffected By P0171 Code

What Are The Possible Causes of The P0171 Trouble Code?

The P0171 trouble code is caused when the air-to-fuel ratio in the combustion chamber is too lean, meaning there is less fuel than oxygen. The vehicle’s computer detects the wrong ratio and alerts the driver by igniting the check engine light.

Possible causes of the P0171 trouble code include:

  • A bad fuel pressure regulator
  • A faulty mass air flow sensor
  • A bad powertrain control module
  • A vacuum leak
  • Bad oxygen sensor
  • Clogged/blocked fuel filter
  • Clogged catalytic converter
  • Clogged fuel injectors
  • Worn-out fuel pump

What Are The Common Symptoms of The P0171 Trouble Code?

Common symptoms of the P0171 trouble code include:

  • Reduced engine power
  • Ignited check engine light
  • Hesitation when accelerating
  • Engine stalling at stop
  • Unable to start or difficulty starting
  • Black smoke from the exhaust
  • Rough idle

Is It Safe To Drive With a P0171 Trouble Code

It is safe to drive with a P0171 trouble code for a short distance only. Driving with the P0171 code will result in a rough ride with poor fuel economy and occasional engine stalling. However, if you drive your car with a P0171 code for an extended period of time, it can lead to catalytic converter damageOpens in a new tab.

How To Diagnose The P0171 Trouble Code

To diagnose the P0171 trouble code:

  1. Scan the vehicle with an OBD2 scanner to verify the P0171 trouble code.
  2. Open the hood but make sure that the engine is turned off. A P0171 code caused by a vacuum leak is audible and you will be able to hear a hissing sound.
  3. Check the fuel pressure sensor and mass air flow sensor with a fuel pressure gauge.
  4. The vacuum and fuel pressure of the engine run at certain specifications in order to maintain a proper air/fuel ratio. Therefore, the reading from the fuel pressure gauge can determine the source of the P0171 code.
  5. Run tests on the mass air flow sensor and the oxygen sensors.
  6. If none of the above tests show any abnormalities, the issue lies with the powertrain control module.

How Much Does It Cost To Repair P0171 Trouble Code

MakeP0171 CodeRepair Cost
ToyotaYes$100 – $500
NissanYes$100 – $500
ChevroletYes$99 – $470
BMWYes$100 – $500
AudiYes$100 – $500
BuickYes$70 – $300
MercedesYes$100 – $600
GMCYes$100 – $500
SuzukiYes$100 – $500
TataYes$60 – $480
LexusYes$100 – $500
MazdaYes$100 – $500
MitsubishiYes$100 – $500
KiaYes$85 – $485
JeepYes$100 – $500
FiatYes$100 – $500
HondaYes$100 – $500
HyundaiYes$100 – $500
OpelYes$72 – $375
FordYes$100 – $500
FiatYes$80 – $400
PeugeotYes$100 – $500

What Repairs Can Fix The P0171 Trouble Code

Repairs that can fix the P0171 trouble code include:

  1. Replacing the fuel pump
  2. Replacing the fuel filterOpens in a new tab.
  3. Replacing the fuel pressure regulatorOpens in a new tab.
  4. Fixing or replacing the powertrain control module
  5. Cleaning or replacing the bad fuel injectorOpens in a new tab.
  6. Cleaning or replacing the dirty oxygen sensorsOpens in a new tab.
  7. Cleaning or replacing the bad mass air flow sensorOpens in a new tab.
  8. Repairing a possible vacuum leak (replacing a broken hose)

Read here on how to reset the P0171 trouble code after repair.Opens in a new tab.

How To Fix The P0171 Trouble Code

Here is how to fix the P0171 trouble code:

  • Test to see if the fuel pump is working. If not, replace it.
  • Inspect the fuel filter. If it’s dirty, replace it.
  • Test the fuel pressure regulator. It is not working properly, replace it.
  • Replace the powertrain control module
  • Test the fuel injectors. Try cleaning them. If that doesn’t fix the problem, replace the bad ones.
  • Clean the oxygen sensor. If that doesn’t fix the problem, replace it.
  • Test the mass air flow sensor. Try cleaning it first. If that doesn’t fix the problem, replace it.
  • Check the air hoses for a possible leak. Replace any damaged hoses.

In Conclusion

The P0171 trouble code means that the engine is running lean in bank one. This means that the bank one (one side of the engine) has an insufficient fuel supply or has too much air in the system. Either way, the cylinders on bank one are low on fuel and high on air which disrupts the perfect air/fuel ratio needed for proper combustion.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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