P0174 – Meaning, Causes, Symptoms, & Fixes

Code P0174 Definition

System too lean (Bank 2).

What Does P0174 Mean?

Combustion engines run most efficiently when they maintain an air-fuel mixture ratio of 14.7 parts air to 1 part fuel. When there are more than 14.7 parts air to 1 part fuel in the air-fuel mixture, a lean condition exists and code P0174 is triggered. The lean condition can be caused by a vacuum leak, which introduces more air into the air-fuel mixture, or by a weak fuel system, which does not input enough fuel into the air-fuel mixture. To keep the engine running properly, the powertrain control module (PCM) tries to compensate for the lean condition by injecting more fuel to the mixture in an effort to maintain the proper 14.7:1 ratio. When these adjustments become too large, code P0174 is triggered.

P0174 Symptoms

  • Check Engine Light is on
  • Lack of power from the engine
  • Rough idle
  • Engine coughing
  • Engine misfiring
  • Faulty oxygen sensor

P0174 Causes

  • Dirty or faulty mass air flow sensor
  • Vacuum leaks – PCV hose, vacuum hoses, intake manifold gasket.
  • Weak fuel pump
  • Clogged or dirty fuel injectors
  • Exhaust leak

Code P0174 Severity – Moderate    

It is okay to drive a vehicle with P0174 for a short period of time, but driving with this code for an extended period of time can overheat the engine and cause internal engine damage.

Code P0174 Common Diagnosis Mistakes

It is important to complete the entire diagnostic process when diagnosing P0174. Many people will replace the air fuel sensor or O2 sensor as soon as they get a bad reading, but the root cause is often a dirty or faulty mass air flow sensor or vacuum leak, thus causing the O2 or A/F sensor to read differently to compensate. Reading and analyzing fuel trims and the freeze frame data is the key to properly diagnosing P0174.

P0174 Diagnosis

Tools Needed to Diagnose:
How To Diagnose P0174:
  1. Use FIXD to scan your vehicle to verify P0174 is the only code present. If other codes are present, they must be addressed first.
  2. Inspect all vacuum lines and hoses for leaks, and make sure they are properly connected. If a leak is present, you will hear a hissing sound, though it may be difficult to hear with the engine running. If you suspect a vacuum leak but are having trouble finding it, check out this detailed guide to finding vacuum leaks.
    • Reconnect any disconnected vacuum lines and replace any damaged vacuum lines that are leaking, then use FIXD to clear check engine light code P0174. If check engine light code P0174 is triggered again, check the rest of the vacuum lines for leaks and continue to the rest of the diagnostic process.
  3. Remove the mass air flow sensor and clean the sensor using mass air flow cleaner or contact cleaner.
    • Reinstall the mass air flow sensor and clear the check engine light using FIXD. If the check engine light comes back on with code P0174 continue the diagnostic process.
  4. If check engine light code P0174 persists after you have reconnected and replaced all damaged vacuum lines and cleaned the mass air flow sensor, perform a fuel pressure test. If any components in the fuel system are failing, replace them as necessary.
  5. If you confirm there are no vacuum leaks, have a clean mass air flow sensor, and your fuel system is functioning properly, it is time to replace the oxygen sensors.
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Comments 9

Rey V

March 10, 2018

This is awesome App. Anyone had a PO455 code reading?


July 13, 2018

Awesome app worth every penny


August 2, 2018

CJ Marco
Aug 2, 17:20 EDT

I just wanted to say thank you for creating this wonderful item. I took my car to shop over a year ago and they told me I need a new intake manifold and it would be over 1500 dollars to fix it. I bought FIXD and plugged it in. It said to check the vacuum lines, fuel filter and mass flow air sensor. I did what the advice of the app said to do and I fixed my problems for less than 150 bucks. WOW. THE CAR IS GREAT. !!!! Just wanted to say thank you

FIXD Marketing

August 3, 2018

Hi Chuck,

At FIXD we have the customer’s best interest in mind and we are thrilled to hear about your experience with your FIXD sensor. We love hearing personal stories from our customers, but don’t keep it to yourself, tell your friends!

The FIXD Team


December 8, 2018

Ok what if im gettin a p0174 and a p0171 for both bank 1 and bank 2 runnin lean. Wich direction should i go first fuel or air


December 22, 2018

Dis you ever figure out on going to fuel or air first?

Kaleb Osburn

January 30, 2019

Ok what if im gettin a p0174 and a p0171 for both bank 1 and bank 2 runnin lean. Wich direction should i go first fuel or air


February 13, 2019

Are you running an aftermarket K&N type air filter? If so, that’s probably why, if not then dirty or faulty Maf, low fuel pressure or clogged injectors.


March 24, 2019

Can a defective pcv valve cause p0174

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