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P0174 - System Too Lean (Cylinder Bank 2)

What is a P0174 Code?

Seeing a check engine light illuminating your dashboard tells you there’s a problem without explaining what or where it is. When your check engine warning light comes on, you can get the information you need to resolve the issue using a scanning tool to check the on-board diagnostics (OBD) system for a diagnostic trouble code (DTC).

Thousands of codes show you the location of your problems and give you the necessary information to diagnose the issue accurately. Moreover, these codes help you know whether the vehicle is safe to drive or needs immediate attention. 

A P0174 engine code indicates that the computer cannot automatically adjust the air and fuel mixture. This code mainly applies to V engines, which have two banks. 

What Does a P0174 Code Mean?

The P0174 code indicates a lean running condition in the engine cylinder’s second bank. The lean condition means the computer has added more air, causing a long-term fuel trim. When you have too much air and insufficient fuel in the air-fuel ratio (AFR), the engine control module (ECM) will detect a lean condition. In an ideal situation, the long-term fuel trim is 1-2%, and the ECM can adjust a lean condition in small amounts. With a P0174 code, it is between 15% and 35%, requiring more compensation than the ECM can handle. Engine Bank 2 is the same side of the engine as Engine Cylinder 2. 

You can safely drive with a lean running condition in bank 2. However, you should know that a leak in the intake system may cause it. This leak can let particles into the engine, which can cause costly damage to your vehicle. 

Potential Causes of a P0174 Code

The P0174 engine code signifies a problem with the air-fuel ratio. Unfortunately, many things can cause lean conditions, and it’s better to have a professional look at your vehicle to pinpoint the exact cause. While the error code does not show the cause of the issue, it offers a starting point for diagnosis. 

Some potential causes of your engine’s lean condition include:

  • An air leak after the mass airflow (MAF) sensor
  • Clogged air filter
  • Clogged fuel injectors
  • Faulty fuel pump
  • Faulty MAF sensor
  • Clogged exhaust gas recirculation port
  • Failing oxygen sensor
  • Leaking brake booster
  • Leaking positive crankcase ventilation (PCV) valve
  • Incorrect fuel pressure
  • Faulty coolant sensor

P0174 Code Symptoms

While driving with a P0174 code is safe, you may experience other symptoms if the problem persists. 

Some other symptoms of issues that cause a P0174 code include:

Vehicles in lean conditions emit nitrogen oxides (NOx), which harm human health and can cause respiratory issues like asthma. Running a car in lean condition causes a misfire, which harms the catalytic converter and ruins the vehicle’s internal parts in the long run. If you notice the symptoms above, have your vehicle diagnosed by a professional to prevent further damage. 

Diagnosing a P0174 Code

When diagnosing a P0174 code, remember that several conditions may contribute to your vehicle’s lean condition. Here are some recommendations for diagnosing a P0174 code.

  • Check for other codes: Look for other DTC codes and resolve them first. Depending on the other trouble codes, the necessary fixes may show you the cause of the P0174.
  • Inspect for vacuum leaks: Check for broken lines, inspect the engine for leaks and pay close attention to the PCV hoses and brake boosters. Ensure the air intake tubing is installed properly and in good condition. You may need a smoke machine to find some hidden leaks.
  • Check the mass air flow sensor: Remove it and look for contamination signs, such as debris that may have passed through the air filters. Oil from changing air filters can stick to the MAF sensor, causing inaccurate signals. 
  • Inspect the exhaust system: A leaking exhaust can affect the oxygen sensor readings. Listen for leaks in the exhaust system and visually inspect it for cracks, damage to the pipes, or black soot spots. Spray soapy water on the hard-to-find leaks. If it forms bubbles, there is a leak in the area. However, leaks behind the rear oxygen sensor do not affect the air-fuel ratio.
  • Check the air-fuel ratio and oxygen sensors: Use a scanning tool to monitor the voltage of the oxygen and air-fuel ratio sensors to ensure they operate correctly. If you don’t have a scan tool, you can use a multimeter. However, vehicles operate differently, so consult your manufacturer’s recommendation for the right procedure to check signals. 
  • Check the fuel pressure: Take a fuel pressure reading and compare it to the factory-listed specifications. Some vehicles have fuel pressure sensors you can use. 

How to Fix a P0174 Code

After diagnosing the code, you must resolve it to have your vehicle operating smoothly. Some of the ways to fix a P0174 code include:

  • Change the faulty oxygen sensors
  • Replace the vacuum lines
  • Clean or change the mass airflow sensors
  • Replace the PCV valve
  • Change the valve cover gasket
  • Replace the brake booster if it has a leak

How Much Does It Cost to Fix a P0174 Code?

A precision diagnosis tells you what repairs are needed to clear the P0174 code. A professional technician will diagnose the problem and give you an estimate for fixing it. The rates will differ depending on your location, car model and the technician’s work. If you only need to clean the MAF, it can cost you as little as $100. Your repair costs may be as high as $1000 for vacuum leaks and $1300 to $1700 for fuel pumps. 

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