Air & Fuel Mixture ControlOBD2 Codes

P0174 – Meaning, Causes, Symptoms, & Fixes

P0174 system too lean (bank 2)

Code P0174 Definition

Bank 2 has too much air or not enough fuel.

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.

What Are The Symptoms Of P0174?

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

What Is The Cause Of P0174?

  • Dirty or faulty mass airflow sensor
  • Vacuum leaks – PCV hoses, vacuum hoses, intake manifold gasket.
  • Weak fuel pump
  • Clogged or dirty fuel injectors
  • Clogged fuel filter
  • Exhaust leak
  • Faulty oxygen sensor
  • Faulty air-fuel ratio sensor

How Serious Is Code P0174? – 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 airflow 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.

Tools Needed To Diagnosis P0174

How To Diagnose Code P0174:

Difficulty of Diagnosis and Repair – 3 out of 5

  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.
  3. 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.
  4. Remove the mass airflow sensor and clean the sensor using mass air flow cleaner or contact cleaner.
  5. Reinstall the mass airflow sensor and clear the check engine light using FIXD. If the check engine light comes back on with code P0174 continue the diagnostic process.
  6. If check engine light code P0174 persists after you have reconnected and replaced all damaged vacuum lines and cleaned the mass airflow sensor, perform a fuel pressure test. If any components in the fuel system are failing, replace them as necessary.
  7. If you confirm there are no vacuum leaks, have a clean mass airflow sensor, and your fuel system is functioning properly, check the exhaust for leaks before the Air Fuel Ratio Sensors or Oxygen sensors if you find any leaks have them repaired.
  8. At this point, if the code still persist you may want to consider replacing your A/F sensor or O2 sensors.

Estimated Cost of Repair

For error code P0174, one or more of the below repairs may be needed to solve the underlying issue. For each possible repair, the estimated cost of repair includes the cost of the relevant parts and the cost of labor required to make the repair. 

  • Vacuum leak $100-$200
  • Clean MAF $100
  • Replace MAF $300
  • Fuel Pump $1300-$1700
  • Fuel pressure regulator $200-$400
  • Exhaust repair $100-$200 (if welded to repair)
  • Air fuel sensor or oxygen sensor $200-$300

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26 Comments

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

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

      1. Excellent app.iam going for vacuum leak or oxygen sensor that light has been on for a week and now 0171ans0174 pop up trucks running fine at idle and great on highway.but could be intake manifold.let you know.God bless

        1. Hoping for a quick, affordable fix for you, Keith!

        2. I had both 0171 and 0174 come up and so before I started to panic, I decided to clean the MAF sensor myself. This eliminated code 0171 for me! Couldn’t believe how dirty it was. Now I can target bank 2 side to diagnose 0174.
          I have saved so much money, and time with this device and app!
          I’ve recommended it to everyone I know that owns a car.
          Thank you to the team at FIXD-you’re awesome!

    2. 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

      1. If your car has over 150K its probably best to replace your Fuel filter (if it hasn’t been already) then clear your codes. If it returns, then go after your fuel pump. Inline fuel filters that get old can clog over time, restricting flow to the engine.

        1. Thanks for the tip, Sammy!

  2. Awesome app worth every penny

  3. 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

    1. 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

    2. 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

  4. 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

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

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

    3. I am having the same problem. Getting both codes tells me it is not the O2 sensors. I have inspected most vacuum lines and they appear in good condition. I have also used fuel injector cleaner and cleaned the Mass Air Flow sensor. My next step is to replace the fuel filter and air filter – much cheaper than the fuel pump. Another possible cause could be a leak in the brake booster $$$$.

  5. 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

    1. 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.

    2. When was the last time you replaced your fuel filter? if its been “years” go after that first, then clear your codes. If they resurface, then go after the fuel pump– if you’ve checked your running fuel pump measurements and they do not match (you can do this with your FIXD Sensor)

  6. Can a defective pcv valve cause p0174

  7. 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 !!!!

    1. Most Probably You Are Right And I Agree With Your Conclusions

  8. Can more than one vehicle be programed into a FIXD unit?

    1. Yes. I have 5 vehicles on one FIXD Sensor

  9. Have a 2000 Cadillac Deville with codes P0171, P0172,P0443 and P00601 . Please where do I start first?

  10. Someone above complained about newer cars, and how annoying they are with codes flashing up. Nobody will disagree I’m sure. Back in the day when auto engines were less controlled, in Southern California, the smog was so thick that it was unhealthy to breathe outside air. On bad days you couldn’t even see clearly across a small street. The worst of all was that some parts of that smog contained nitrogen oxides. Those oxides can build up in your bloodstream and kill you if it adds up to enough concentrated amounts.
    Older cars were less expensive to maintain, were more simple. They burned inefficiently as well as real “dirty”. If nobody ever changed the way cars ran, now being at least 40 years later, everyone would either be stuck inside forever, or go outside and take a chance on choking to death.

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