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 14

Rey V

March 10, 2018

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

Randall Rapier

May 3, 2019

This the best device and service I’ve come across in a long time .Thanks to all at FIXD. RANDALL

Louie

May 12, 2019

I have a 2003 nissan altima v6 se and was getting po171 and po174 so i change my maf sensor and it was ok for a day then the next it didn’t want to start later in the it did and them got a po300 and it was a rough idle and felt like mottor was working hard so i change all my spark plugs and coils and still the same problem now car hiccups well accelerating like at 40 or 60 and the p0171 comes om with kmow check eingen light just tge cod then cheak engine light gos on ant its the p0174 i check for imtake manifold leaks air leaks i spayed carb cleaner and know change of ideil and cheak the fule injectors with a screw driver and there all working do u thing it could be a fuel pump it tyrmd off on me like to times today

Bob

July 13, 2018

Awesome app worth every penny

Chuck

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

Brad g

June 12, 2019

I keep getting code p0174 only when car is warmed up and getting on the freeway! It’s the only code that keeps coming back. I reset the code it drives awhile no problem, then go get on freeway and it sets again. Toyota Camry 2003

Destin

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

Frank

December 22, 2018

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

Randall Rapier

May 3, 2019

This the best device and service I’ve come across in a long time .Thanks to all at FIXD. RANDALL J.

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

Keith

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.

Ivailo

March 24, 2019

Can a defective pcv valve cause p0174

TRUTH.U. CANT HANDLE

July 25, 2019

MODERN CARS SUCK. PASS IT ON FOR THE STUPID AND GULLIBLE.

CARBURETORED CARS NEVER HAD THESE STUPID INSANE CONFUSING PROBLEMS!!!!

All these forced upon us sensors by the EPA and automakers lying about big hp gains. F U !!!!

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