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System Too Lean in Bank 2 – What is the Cause?

System Too Lean in Bank 2 – What is the Cause?

You are driving down the road and notice a diagnostic trouble code in your car pop up – the P0174 OBD-II trouble code. You’re thinking to yourself – what is that? It refers to the system too lean bank 2 issue. You’ve never seen it before and certainly never even heard of it. Let’s dive a little deeper into what this means, how you can fix it, and the diagnostic procedures you can take to ensure this trouble code does not show up again during your driving.

Auto Repairs Are EXPENSIVE


Although the P0174 OBD-II code is not specific to certain manufacturers and is considered a generic code that can show up in any type of car, regardless of make, model, or year, it can be more common for certain drivers more times than others. More specifically, a P0174 OBD-II code is most often reported in specific Chevy and Ford cars. 


If you are driving one of these cars and your vehicle is triggering a P0174 OBD-II code, let’s help you figure out how you can learn a little bit more about what this problem is and how you can fix it and diagnose it. By learning about this code, you can figure out the issues with your car’s system too lean in bank 2. 

Meaning of the P017 OBD-II Code


The diagnostic trouble code P0174 OBD-II stands for “System Too Lean (Bank 2).” This code shows the driver or the mechanic that the car’s internal computer has detected a lean running condition. 

Lean Condition

So what is a lean running condition? An imbalance of the air brings on a lean condition to fuel ratio due to either a lack of fuel or too much air entering the engine during driving. The bank 2 section of the code shows that the main issue lies within the engine’s concentrated side opposing the #1 cylinder.


The main error codes that show up in cars for lean conditions and the system being too lean for bank 2 are both P0171 and P0174. The P0171 is caused by a lean condition in cylinder bank 1, while the latter code, the P0174 code refers to the system being too lean in bank 2.

Engine Control Module 

Even though the engine control module is supposed to do its job and bring a lean condition back to the normal condition, it can only do this so much. This is true of any part – it can only do its job up until a certain point and to a certain extent, it won’t be able to continue fixing the issue if it is too prevalent and consistent. 


Therefore, the P0174 code might be needed to let the driver or the mechanic know that it is time to resolve this problem before it gets too late and the system becomes even leaner in bank 2. 

Combustion Engine Function

In order to get a better understanding of what a lean condition really is about a car, let’s talk a little bit more about how a combustion engine functions within a vehicle. In the ideal conditions for any car, the air to fuel ratio being burned and ignited by the engine is approximately 14.7 parts of air to 1 part fuel, creating a 14.7:1 ratio.


When the ratio of air is too low and the fuel ratio is higher than it should be in the car, this can result in something called a “rich” mixture – the exact opposite of a lean mixture. If there is too much air and not enough fuel, you have what we would call a “lean” mixture, causing the system too lean in bank 2.  

Fixing an Imbalanced Mixture

To fix the imbalance of the air to fuel ratio, the electronic control module works in tandem with the oxygen sensors within your car to determine the necessary amount of oxygen needed and the current amount in the exhaust. The electronic control module can then regulate the air and fuel mixture by adding or reducing the fuel to get the right ratio, thereby reducing the chances of having a system too lean for bank 2. 


So, what are the signs that your engine is running lean and you need to fix the system too lean for bank 2? 

Signs of System Too Lean Bank 2


It is crucial to recognize when your engine is running lean to maintain the health of your car and prevent any further issues within your vehicle. Here are a few main signs that your system is too lean in bank 2. 

  • Poor Car Performance

First, if your car is performing poorly and can’t drive like it is supposed to or like you are used to, this is a sign of a system running lean in bank 2. Your car will have less power than it had before, less acceleration, less punchiness, and less driveability. For example, this could also refer to sluggish acceleration, lack of performance at certain RPMs, or an overall lack of power in your vehicle. 


This is the result of a lack of fuel within the ignition chamber, at a much lower value than your car’s computer expects or is used to running on, causing the power to be less than usual. If your car is running extremely lean in bank 2, then your car might even backfire or sputter when decelerating. 

  • Trouble Starting Your Car

Second, a sign that your engine is running lean and the system is too lean on bank 2 is that you may run into trouble when starting your car, and your engine might not turn over. This could be because your initial ignition might not be enough to sustain combustion or that your engine might not be able to generate the power needed to turn the crankshaft, resulting in the crankshaft getting stuck. 

  • Spark Plugs are Discolored

The third reason and sign that your engine is running lean on bank 2 is that your spark plugs are clean or white. Spark plugs should generally be brown or a dark color to the eye, caused by normal ignition and the correct firing. However, your spark plugs will become too clean or white when your bank 2 system is too lean. 

Causes of System Too Lean Bank 2 


There are various causes to the system being too lean in bank 2 within your car, causing performance decreases and the potential for further problems within your vehicle.

  • Faulty Mass Airflow Sensor

The first cause of the P0174 code and the system is too lean is a dirty or faulty mass airflow sensor. The mass airflow sensor is one of the key components of an electronic fuel injection system in your car. It is installed between the air filter and the intake manifold. A contaminated mass airflow sensor’s symptoms are the inability to measure the amount of air flow correctly. 

  • Vacuum Leaks With Car Hoses

The second cause of the system too lean in bank 2 is vacuum leaks with the PCV hoses, vacuum hoses, or the intake manifold gasket. This leak can occur anywhere between the engine and a mass airflow sensor, causing unmetered air to enter the system. The excess air causes the actual airflow to be higher than the mass airflow sensor measures, miscalculating the amount of injected fuel and causing the engine to run lean. 

  • Damaged Fuel Pump

The third cause of the system being too lean is a weak fuel pump. There are many signs of a weak fuel pump, like the engine sputtering at high speeds, rising temperature, fuel pressure gauge misreading, loss of power when the vehicle is stressed, surging, and decreased gas mileage.

  • Clogged Fuel Injector

Additionally, another cause of the lean fuel system is a clogged fuel injector. Symptoms of a clogged fuel injector are starting issues, poor idle, failed emissions, poor performance, not being able to reach full RPM, increased fuel consumption, rough engine performance, and surging and bucking under various loads. 

  • Failed Fuel Pressure Regulator 

The next reason for the system being too lean in bank 2 is a failed fuel pressure regulator. A failed fuel pressure regulator’s symptoms are a misfire and decrease in power, acceleration, fuel efficiency, fuel leaks, black smoke from the exhaust, and regulator leaks. 

  • Powertrain Control Module Issues

The sixth cause of the system too lean in bank 2 is PCM issues, like the software needing an update or other computer-based issues. The PCM’s main failure symptoms not working correctly is the check engine light turning on, the car not being able to start, the mileage suddenly dropping, your engine stuttering, erratic or random shifting, receiving a PCM error code, or other computer based glitches. 

  • Damaged Oxygen Sensor

Another cause of the system too lean in bank 2 is that there is a worn-out oxygen sensor. The first symptom of worn out oxygen sensors is the check engine light coming on, along with poor fuel economy, rough idling, weak engine performance, and a failed emissions test. A damaged oxygen sensor can cause a system too lean in bank 2 warning in your vehicle. 

  • Contaminated Oil Sensors

The last cause of the system being too lean in bank 2 is that the use of oiled filters could cause the sensor to become over-oiled and contaminated throughout the lubrication process. Contaminated oil sensors will set off any warnings to your system that are too lean in bank 2. 

System Too Lean Bank 2 Repair Cost


For the error code P0174, you might have to have at least one, or a combination of multiple, of repairs done in order to fix the underlying issue. To fix a vacuum leak, the cost is between $100-$200, while the cost to clean a MAF is $100 and the cost to replace the AMF is $30. 


Fixing the fuel pressure regulator is between $200-$300, while fixing the exhaust repair is between $100-$200. 

Diagnosing the System Too Lean in Bank 2 

  • Use a Diagnostic Tool

The first step in diagnosing your code P0174 is that you will need to use a scanner to scan your vehicle and make sure that the P0174 is the only code showing up in the diagnostic trouble section. If other codes are illuminated or showing up, then you must address those problems first and foremost.

  • Inspect Hoses For Leaks

The second step in diagnosing the code that shows your engine system is too lean in bank 2 is that you will need to inspect all vacuum lines and hoses for leaks, making sure they are properly connected. If you suspect a leak or can feel the leak in one of the fuel lines, you will hear a hissing sound and feel the air escaping. If you suspect a vacuum leak but can’t find it, then you should make sure you can take your car to a mechanic.

  • Reconnect Vacuum Lines

Next, reconnect any vacuum lines you have taken apart and replace any damaged vacuum lines that are leaking, using a scanner to clear the check engine light code P0174 to fix the engine running lean on bank 2. 

  • Clean MAF Sensor

After you have used the diagnostic trouble code scanner, remove the mass airflow sensor and clean the sensor using contact cleaner to ensure there is no debris or unwanted particles. 

  • Clear the Check Engine Light

After you clean the sensor, reinstall the mass air flow sensor and clear the check engine light. If the check engine light code P0174 continues after you have replaced the damaged vacuum lines and properly cleaned the mass air flow sensor, perform a fuel pressure test.  If there are no clear vacuum leaks, you have a clean sensor, and the fuel system is working well, you have successfully fixed your system being too lean in bank 2. 


Determining the causes of the system too lean in bank 2 can help you figure out the total repair or replacement cost for this part in your vehicle!