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P0174 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


Trouble code P0174 proper definition is that your “system is too lean.”


Trouble code P0174 will opulate when the engine control module (ECM) detects a lean condition in the vehicle. “Lean condition” means that there is too much air and not enough fuel in the vehicle’s air to fuel ratio (AFR). One of the many functions of a vehicle;s ECM is to adjust the lean operating conditions of your vehicle back to a normal ratio, but it will only do this in small to moderate amounts. Trouble code P0174 will populate on your OBD2 if the air fuel ratio of your vehicle requires more compensation or a greater adjustment than your ECU is capable of handling.


There are a few primary causes that can create trouble code P0174 to read on your OBD2 scanner:

  • There is an air leak in your system, after the mass air flow sensor (MAF). This can be a torn intake boot or a faulty intake manifold gaskets.
  • That you have a fautly or dirty mass air flow sensor.
  • There is a faulty oxygen sensor in your vehicle.
  • That the vehicle is experiencing incorrect fuel pressure.
  • That the vehicle may have a leaking positive crankcase ventilation (PCV) valve.
  • That the vehicle has a clogged exhaust gas recirculation port (EGR).
  • That the vehicle has a leaking brake booster.

Any of these issues can lead to a P0174 trouble code. If you suspect you may have any of these problems with your vehicle, it is going to take a skilled mechanic and a thorough diagnosis to properly fix the issue.


There are a few common symptoms a vehicle will experience if a P0174 trouble code is present on your OBD2 scanner:

  • You may notice that the vehicle is experiencing increased fuel consumption.
  • The check engine light will come on to indicate there is a problem.
  • The vehicle is experiencing a high or rough idle.
  • There is a decrease in the vehicle’s ability to accelerate.
  • If you notice that the engine is stalling regularly.

These are some of the most common symptoms you will notice if a vehicle is experiencing a P0174 trouble code.


There are several essential steps that a mechanic will need to go through to properly diagnose that a P0174 trouble code is verified:

  • They will need to perform a fuel pressure test to verify the fuel pressure of the vehicle.
  • Check the vacuum lines and intake system for leaks.
  • Inspect the valve cover for leaks and/or for worn hoses.
  • Inspect the PCV valve to make sure it is working properly and that it isn’t damaged or faulty.
  • Use a scan tool or multimeter to test the mass air flow sensor.
  • Use a scan tool or multimeter to test the related oxygen sensor.

Common mistakes

Some of the most common mistakes that are made when working to fix the vehicle and clear a P0174 trouble code are: 

  • Replacing a component that could be working properly, without testing it first to see if it is faulty or having issues.
  • Failing to check the intake system or overlooking the intake system for leaks and/or tears.

How serious is this?

In general, a P0174 trouble code is not that serious. However, you should be aware there is a possibility that the lean condition of the vehicle is being caused by a leak in the intake system. If that is the case, leaks in the air intake can allow foreign particles to enter the engine, which may be damaging to the vehicle.

What repairs can fix the code?

These are some of the most common fixes for clearing a P0174 trouble code:

  • Replace the mass air flow sensor.
  • Replace the faulty oxygen sensor.
  • Replace the PCV valve.
  • Replace the vacuum line. 
  • Cleaning the mass airflow sensor.

Related codes

None listed.


If you notice a P0174 trouble code on your OBD2 scanner, the underlying issue that is causing this error code may or may not be urgent. With that being the cause, an experienced mechanic should properly investigate and diagnose the problem as soon as possible, paying close attention to common mistakes that are made when inspecting this trouble code.

P0174 Code – What Does It Mean & How To Fix It