BMW code P0171| How to diagnose and Fix


Engine error BMW code P0171 is in the DTC system, which is a common error code that appears on some BMW engines. This code indicates a potential problem in the fuel system. In this article, Eurocartool will present the symptoms, causes, remedies and severity associated with P0171.

What does the BMW code P0171 mean?

Code: P0171
Definition: P0171 – System Too Lean (Bank 1)
Error code P0171 on BMW engines is a form of diagnostic trouble code (DTC) indicating that the engine computer (DME) judges the engine to be running too lean in bank 1, especially cylinders 1-3 in case of 6-cylinder in-line engines. This condition typically occurs when the air-fuel ratio (AFR) causes the fuel mixture to become too lean, meaning there is too much air and too little fuel in the mixture.

Notably, this error code usually does not mean the engine is running poorly. Instead, DME recognizes the problem and automatically adjusts by injecting more fuel to make the mixture richer. This could mean that the engine is actually working harder and has a higher ratio of fuel to a given amount of air.


Is code P0171 dangerous?

BMW code P0171 is assessed as having medium severity. Although not an extremely serious problem, some symptoms can affect performance and driving experience. It is important to judge and handle the problem carefully. If your BMW feels unusual or unstable, it should be checked immediately and the vehicle may be towed to avoid an unwanted situation.

Although P0171 is not usually considered an extremely serious problem, it should be noted that if the engine is running too hard, DME will inject more fuel, resulting in an unbalanced air-fuel ratio. This can cause wear and tear on the catalytic converter, which is not a cheap part. Additionally, if the problem persists, it can cause serious damage to the engine, especially since too little fuel leads to increased heat and can harm pistons, valves, and other components.

P0171 bmw code Symptom

Symptoms of BMW code P0171 often include:

  • LampCheck Engine glow:An illuminated check engine light is one of the most common symptoms, often alerting drivers to a problem.


  • Power loss: Power loss may occur, especially when the engine is operating in undesirable conditions.
  • Difficult starting: The engine may start to idle and become unstable, especially when under light load or at a standstill.
  • Misfire (misfire): Code P0171 can be associated with misfire, when one or more cylinders do not operate correctly.
  • Slow starting/long crank: Starting may become slow and it may take longer for the crank to crank the engine.

Depending on the specific cause of BMW code P0171, symptoms may vary. Problems such as loss of power, misfires, and poor starting performance can be a sign of a serious problem that requires prompt care and repair from a professional mechanic.

Code p0171 BMW Reason

Error code P0171 on BMW engines can come from many different causes. Here are some common causes:

  • Faulty O2 sensor: The O2 sensor measures the amount of oxygen in the exhaust and sends information to the engine control system. If the sensor is faulty, inaccurate information can result in an incorrect air-fuel ratio.
  • Defective fuel injectors: One or more fuel injectors that are not functioning properly can increase the air-fuel ratio.
  • Intake air leak near the cylinder head: A leak in the intake air system can increase the amount of air, changing the air-fuel ratio.

It is worth noting that the problem may be focused on a specific engine range. For example, if cylinder 1’s fuel injector fails, error code P0171 will only affect bank 1 without triggering error code P0174 bank 2.


If both error codes P0171 and P0174 appear, possible causes include pre-manifold air leak, low fuel pressure, positive crankcase ventilation (PCV) leak, valve cover leak, and gasket, mass air flow (MAF) sensor or vacuum leak. These problems can affect both engine ranges.

Instruct diagnose and repair P0171 code errors

If you deal with error code P0171 on your BMW, the first thing is Use ISTA D software with ICOM Next or OBD scanner to determine the cause. After confirming and clearing the error codes, driving for about 15 minutes can help you check if they come back or not. If the error code reappears, it may be a sign of a specific problem that needs to be diagnosed.

In cases where P0171 and P0174 appear together, PCV (or CCV) and a vacuum leak are usually the common cause. If there is only P0171, the O2 sensor is usually the main cause. However, it is most important to take diagnostic steps to determine the exact problem.

Diagnose error code P0171 on your BMW

The following quick list can help you diagnose error code P0171 on your BMW:

Step 1. Check all error codes stored in DME to make sure you haven’t overlooked any other problem.
Step 2. If a fuel code is present, start with a fuel system diagnosis.
Step 3. Check basic components such as vacuum hoses and wires, as they may come loose.
Step 4. Smoke testing can be an effective method to detect vacuum or PCV related problems.

Fix the BMW P0171 code error

In addition, you can usually fix the BMW P0171 code error as follows:

  • Replace the fuel filter or fuel pump
  • Replace the powertrain control module
  • Change fuel pressure regulator
  • Replace the high air flow sensor
  • Change injectors
  • Replace the oxygen sensor
  • Repair vacuum leaks

Always start with the basics before considering replacing parts. Sometimes, the problem is simply a hose or wire that has come loose. You may consider replacing inexpensive parts such as vacuum hoses to prevent future problems.

With detailed instructions from how to recognize to how to fix, you can quickly fix error BMW code P0171 quickly. If you have not prepared enough tools or software or diagnostic equipment, or have difficulty during the implementation process, please contact us VIA WhatsApp: +13155472355 to receive direct support from Eurocartool experts.