What does the P0171 OBD-II code mean?

For engines to run efficiently, they maintain the manufacturer’s optimum air-fuel mixture ratio, and when this doesn’t happen, a lean condition exists, triggering a P0171 code. This lean condition occurs when the engine is receiving either too little fuel or too much air. The cause is either a weak fuel system on the engine’s first bank that doesn’t add sufficient fuel in the air-fuel mix or a vacuum leak introducing more air into the mixture.

How serious is the P0171 code?

This particular OBD-II code is considered a serious issue as the engine is not maintaining the correct fuel/air ratio resulting in a significant waste of fuel and a lack of power when driving. As long as the P0171 fault code is stored in the powertrain control module, the vehicle’s engine will simply not run well at all and damage to the catalytic converter may occur if the code is stored for an extended period. As such, it is highly recommended to have the code diagnosed and repaired as soon as possible to ensure your vehicle runs efficiently and smoothly. 

What are the common symptoms of a P0171 trouble code?

When a P0171 OBD-II code is triggered, symptoms may include the following:

  • Check Engine light illuminated
  • Vehicle may be difficult to start
  • Loss of power from the engine
  • Rough idling
  • Acceleration surge or hesitation
  • Engine misfiring

What are the causes of a P0171 OBD-II code?

There are multiple causes for the P0171 trouble code to be triggered, including:

  • Defective or dirty mass airflow sensor
  • A weak fuel pump
  • Clogged fuel filter
  • Faulty, clogged or dirty fuel injectors
  • Vacuum leak (PCV and vacuum hoses)
  • Leaks in the air intake system
  • Intake manifold gaskets leaks
  • Exhaust leak
  • Defective fuel pressure regulator
  • Faulty air-fuel ratio sensor
  • Defective oxygen sensor
  • A faulty powertrain control module (PCM)

How to diagnose a P0171 OBD-II code?

The simplest way to diagnose an OBD-II fault code is to use an OBD-II scanner or book a diagnostic check with a trusted mechanic or garage. 

  • It is essential to see whether any technical service bulletins are available for your vehicle’s make and model and check if there is a known issue that can help solve the problem.
  • Scan the system for other OBD-II codes. 
  • Clear the fault codes, followed by a test drive of the car while reading the live data on an OBD-II scanner.
  • If the code persists, check the engine for vacuum leaks with a vacuum gauge or visually inspect the vacuum lines for leaks. 
  • Test the fuel pressure using a fuel pressure gauge.
  • Check the mass airflow sensor for dirt and functionality.
  • Check the exhaust for leaks
  • Test the air-fuel ratio sensor or oxygen sensors using the manufacturer’s procedures.

How to fix a P0171 diagnostic code?

It is advisable to test drive the car after each check/work is performed to see if the fault code clears:

  • Confirm the code with an OBD-II scanner, followed by a reset, ensuring no other diagnostic codes exist. If there are other codes present, these must be addressed first.
  • Follow this with a test drive of the car to see if the trouble code clears. 
  • Repair, replace any damaged or loose hoses (PCV, Vacuum, intake manifold gaskets)
  • Clean the mass airflow sensor
  • Clean the fuel injectors
  • Replace the fuel filter
  • Replace the fuel pump
  • Replace the fuel pressure regulator
  • Replace fuel injector (one or more)
  • Replace oxygen sensor (one or more)
  • Replace mass air flow sensor
  • Replace powertrain control module (PCM)

How to avoid a P0171 Trouble Code?

Whilst failed parts that are out of your control may be the culprit of a P0171 code; it is always good practice to maintain your vehicle’s engine in good working order. This includes regularly servicing your car and, in between services, making visual inspections of hoses and lines to ward off vacuum leaks and to maintain your engine in a good clean condition generally. By frequently undertaking maintenance checks and cleaning will ensure your vehicle remains in good running order as much as possible.

About Fixter

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