P0174 Code: System Too Lean (Cylinder Bank 2)


The P0174 error code in your vehicle indicates that the engine is working in the lean condition. The lean condition means that there is more oxygen or air than the required amount of fuel in the cylinder. This indicates that there is an incorrect ratio of air and fuel in the engine of the car especially in bank 2of the cylinder.

Definition of P0174 error code

This is the OBD-II generated error code that means that the upstream oxygen sensor is biased towards the air in the air-fuel ratio.

What is the PO174 error code mean?

The error code P0174 ECM is detecting the lean condition in the vehicle. The engine control module adjusts the leans condition in small to the mediocre amount. If the air-fuel ratio is more required to return to its normal condition then ECU generates the P0174 error code.


The PCM of the vehicle pays attention to the fuel delivery for the proper functioning of the engine and ensures that the engine is in good condition and will require an air-fuel ratio of 14:7:1. The computer of the vehicle adjusts the injector pulse to regulate the flow of fuel that is required by the vehicle.


The oxygen sensors send this information to the computer and determine the quantity of fuel required to run the engine smoothly. The computer sets the fuel flow to maintain the correct ratio of the air-fuel combustion. If the computer does not fulfill the air-fuel ratio then it generated the error code P0174.

Possible causes of P0174 error code?

You may notice various reasons that can generate the P0174 error code in your vehicle. Some of them are:

  • Faults in the mass airflow sensor
  • Faults in oxygen sensor
  • Inappropriate fuel pressure
  • Leakage in positive crankcase ventilation (PCV) valve
  • Blockage in exhaust gas recirculation (EGR) Port
  • Leakage in the brake booster

Symptoms of error code P0174

  • Increment in fuel consumption
  • Check Engine Light illuminates
  • Rough or high idle engine
  • Hesitation in acceleration
  • Engine stalling while starting
  • Lack of power while starting the car
  • The spark occurs while ignition of the engine

The severity of the P0174 error code

The lean condition of the vehicle is not as serious as compared to other error codes. But, the lean condition can cause leakage in the air system that affects the performance of the engine. The leakage in the engine will allow foreign particles to enter the engine chamber that can lead to damage to the engine.

How to detect the P0174 error code?

When you find that your check engine light is on, you can use OBD-II to detect the generated error code. If the monitor shows the error code then it is clear that the computer is unable to fulfill the air-fuel ratio that helps to run the engine smoothly. Follow these steps to diagnose the exact reason for the generated error.

Detect the Vacuum leaks

Check the vacuum cracks thoroughly the vacuum lines. Through the cracked vacuum line air enters and leads mixture code. Sometimes the gaskets get cracks and that results in vacuum leaks. And this will rise in engine’s idle speed.

Test for Exhaust Leaks

Leakages in the exhaust system cause the leaning condition because the air enters through the exhaust vents. You can check leakage in the exhaust system by hearing the noise while the vehicle running in idle condition for 1500 rpm.

Test the service mass air-fuel sensor

If you have an old vehicle and you drove for miles, then the filaments of mass air-fuel sensors get contaminated due to the impurities in the air. That leads to false reading and maybe a cause for the generation of this error code. Remove the impurities from the filaments using sensor safe carburetor cleaner.

Test the Oxygen Sensor

Check the oxygen sensors if they are working properly or not. If there is some problem in the working of the oxygen sensors it will give wrong feedback information that causes the lean condition.

Test the spark plug

Due to the lean condition, when the engine misfires, clean oxygen is sent to the exhaust system of the engine. This can lead to severe sparks in the spark plug during the working of the engine.

Test the Air Intake Boot Replacement

When there is a problem in the air intake boot transports the throttle in the accelerator occurs. If there is any problem in the air intake the false reading is flashed in the mass airflow sensor tool code.

How to fix this error code?

When to detect the P0174 error code in the vehicle then you need to clean your MAF sensor. The perfect way to cleanthat sensor is to take it off using a brake cleaner or electronic cleaner. You need to take care while cleaning the sensor as it can cause damage to the sensor.

When you are done with all the repairs, clear trouble codes and reset by driving the vehicles to get the correct functionality of the vehicle.

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