P0171 Trouble Code: System Too Lean (Bank 1)

A sufficient supply of air and fuel to the engine cylinder is very important for the proper operation of the engine. When the air-fuel mixture contains too high air or too low fuel, it is known as a lean condition. The lean or rich condition is very dangerous for your engine. When your powertrain control module monitors a lean condition in Bank 1, it triggers the diagnostic trouble code (DTC) P0171. This article explains the P0171 code causes, symptoms, and its fixing cost.

P0171 Code Definition

The P0171 trouble code stands for “System Too Lean (Bank 1).”

In the definition, Bank 1 indicates the side of the engine that contains the cylinder number.

What does the P0171 Code Mean?

The P0171 code indicates that your powertrain control module (PCM) detects a lean running condition on the first bank of the engine.

A lean condition occurs when your vehicle’s air-fuel mixture has too much air and insufficient fuel.

P0171 code

The vacuum leaks may also lead to lean conditions. A vacuum leak introduces more air into the air-fuel mixture, which leads to a lean condition. To ensure the efficient working of your vehicle, your PCM also assists in compensating for the lean condition by injecting more fuel into the mixture in an effort to maintain the proper 14.7:1 ratio.

Internal combustion engines run most efficiently when they maintain an air-fuel mixture ratio of 14.7:1. When there are more than 14.7 parts air to 1 part fuel in the air-fuel mixture in the first bank of the engine, a lean condition exists, and code P0171 is triggered.

Causes of P0171 Code

Symptoms of P0171 Code

  • Check engine light illumination
  • Engine misfiring
  • Poor engine performance
  • Engine stalling
  • Hard to start the engine
  • Rough idling
  • Your catalytic converter may go bad if you don’t fix this code on time.
  • Poor fuel economy

Read More: P0174 Code Symptoms and Causes

How to diagnose the P0171 Code

  • Use an OBD-II scan tool to confirm the existence of the P0171 code. If other codes are present, you should fix them first. Clear the codes saved in the PCM memory and perform a test drive to see what comes back.
  • Perform a fuel pressure test to check the fuel pressure. To maintain a proper air-fuel ratio, the vacuum and fuel pressure of the engine should be according to the manufacturer’s instructions.
  • Inspect the fuel pressure sensor. If your fuel pressure sensor is damaged, immediately replace it.
  • Check the fuel system for a blockage or damage
  • Check the intake system and exhaust system for leaks
  • Inspect the fuel tank to check the fuel level. Add more fuel if the fuel level is less than a specific limit.
  • Inspect the fuel rails for damage or blockage
  • Inspect the fuel injectors for damage
  • Properly inspect the oxygen sensors installed on Bank 1
  • Inspect the valve cover for a leak or worn hoses
  • Properly inspect the mass air flow sensor for a damage
  • Inspect the PCV valve for corrosion or damage
  • Reprogram or replace the PCM if needed

Common P0171 Code Diagnosis Mistakes

  • Replacing the engine sensors without inspecting the wiring and connections
  • Replacing the unnecessary parts
  • Replacing the parts without testing them
  • Not cleaning the blocked or dirty fuel rails, MAF sensor, or fuel injectors.
  • Not clearing the PCM memory after fixing the codes

How serious is the P0171 Code?

The P0171 code is considered a serious trouble code. Driving with this code is very dangerous. This code may produce different performance problems that may damage your engine parts. If your car’s engine doesn’t maintain a proper air-fuel ratio, you may face poor fuel economy and engine misfiring issues.

Driving with P0171 or P0174 for a long time may cause damage to your car’s catalytic converter, which is very expensive to repair or replace. Therefore, you should fix this code as soon as possible.

Repair Cost for P0171 Code

The repair cost of the trouble code P0171 varies according to the vehicle model, your living area, and labor cost. To fix this code, you need one or more of the below-given repairs:

PartsRepair Cost
Vacuum leak repair$90 to $220 
Spark plug replacement$180 to $270
MAF sensor replacement$100 to $320
Fuel Pump replacement$220 to $1,090
MAF sensor cleaning$80 to $110
Exhaust gas leak repair$120 to $300
Fuel pressure regulator replacement$280 to $480
O2 sensor replacement$320 to $410 

FAQ Section

Can I drive with the P0171 code?

Yes, you can drive with the P0171 trouble code, but it is not recommended. Actually, this code generates various performance issues, such as engine stalling, poor acceleration, engine misfiring, or poor fuel economy. These issues may lead to expensive damage.

Driving with a lean fuel trim code for a long period of time can also damage the catalytic converter of your car. Replacing a catalytic converter is expensive. Therefore, you shouldn’t drive with P0171.

What repairs can fix the P0171 Code?

  • Replacing or cleaning the MAF sensor
  • Cleaning the clogged fuel rails
  • Replacing the faulty EGR valves
  • Cleaning the EGR system
  • Replacing the damaged brake booster
  • Replacing the bad O2 sensor
  • Fixing the vacuum leaks
  • Replacing the faulty PCV valve
  • Replacing the damaged vacuum lines
  • Inspect the fuel level and add more fuel if needed
  • Fixing the exhaust leaks
  • Replacing the faulty fuel injectors
  • Reprograming the PCM

Can a bad PCV valve cause P0171?

Yes, a bad PCV valve is one of the major causes of the P0171 code. However, your PCM may trigger this code due to many other reasons, such as a bad MAF sensor, insufficient fuel, low fuel pressure, or a vacuum leak.

Can a bad oxygen sensor trigger the P0171 Code?

Yes, a faulty oxygen sensor may lead to a lean condition and trigger the P0171 code. The real problem isn’t a faulty O2 sensor, but a faulty fuel injector, a bad MAF sensor, a vacuum leak, or low fuel pressure may also cause the engine to run lean.

What causes code P0171 in a Chevy?

One or more of the below-given causes may trigger the P0171 code in your Chevy:

  • A bad fuel pressure regulator
  • A faulty O2 sensor at Bank 1
  • A bad fuel pump
  • Insufficient or dirty fuel
  • Vacuum leaks
  • Damaged or clogged fuel filters
  • Clogged or faulty fuel injectors
  • Exhaust leaks
  • Clogged fuel rails
  • A faulty MAF sensor
  • A leaky PCV valve
  • A faulty air-fuel ratio sensor
  • Bad PCM
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