P0171 code subaru forester

P0171 code subaru forester DEFAULT

One of the most common trouble codes with the Subaru Forester is the P code. This code number references a number that is given to you when you plug your car into a OBDII scanner. It&#;s not the most complicated OBDII trouble code to diagnose. It is also one of the most common.

 

P Fuel Trim System Lean Bank 1

Forester P Code Defined

Subaru Forester P Code Symptoms

P is an OBDII trouble code. The code technically stands for:

Fuel Trim System Lean Bank 1

The code is thrown when the oxygen sensors detect that there&#;s not enough oxygen in the exhaust system. This is commonly referred to as a &#;lean&#; condition.

The vehicle&#;s ECM will add more fuel to the mixture in order to bring the air fuel mixture where it needs to be for optimal combustion. It also throws the code P to let you know that it has done this.

 

Forester P Code Symptoms

P Subaru Forester

The P code on a Subaru Forester will often be thrown if the fuel injection system is not operating properly. Typically the code will be triggered by a lean condition in the engine.

There aren&#;t usually any drivability issues associated with P For most people the first sign that anything is wrong at all is the service engine soon light coming on.

Here are the typical symptoms that something is wrong when you have code P

  • Mileage- may or may not suffer depending on how much the air fuel mixture has changed.
  • Misfire&#; If the air fuel mixture has gotten too far from factory specs, this can cause the Forester to misfire.
  • Idle Issues&#; With the air/fuel mixture altered, the vehicle can idle erratically as the computer compensates to keep the engine running.

This youtube video is a great resource for diagnosing the P trouble code in your Forester.

Top Subaru Forester P Causes

P Subaru Forester Symptoms

There are many things that can cause the P trouble code on the Subaru Forester. Here are the most common ones.

  • Vacuum Leaks&#; With the Subaru Forester, one of the most common cause for the P code to show is a vacuum leak. Take a look around and see if you can find the vacuum leak. Here&#;s a great YouTube video on how to find a vacuum leak.
  • Oxygen Sensor&#; The P codes is thrown when the oxygen sensor(s) do not register enough oxygen in the exhaust. When the oxygen sensor is bad, it can cause a false reading and trigger the code. The computer will still adjust the air/fuel mixture to compensate. This will cause the Forester to run rich.
  • Mass Air Flow Sensor&#; The mass air flow sensor calculates the volume of air entering the engine. If it has gone bad, the air fuel mixture will be off and the P code will show.
  • Bad Fuel Injectors&#; If you have one or more fuel injectors that have gone bad that can certainly cause the air/fuel mixture to go bad.
  • Fuel Pump/Fuel Filter&#; Today&#;s modern fuel injected motors need a lot of fuel pressure to atomize the gas properly. If the fuel pressure is not as high as it needs to be this atomization doesn&#;t happen properly and the optimal air/fuel mixture isn&#;t achieved.
  • Air Filter&#; While it&#;s not the most common reason to throw the P code, a clogged air filter certainly can cause the code to throw. And, since it&#;s so easy to check, why not look?

Good luck figuring out what is wrong with your Forester. If there are any inaccuracies, or anything that you feel could improve the article, please feel free to comment or message. Thank you.

Categories Subaru ForesterSours: https://wwwr4transmissionhq.com/psubaru-forester/

Thread: P System Lean FIXED!

  • ,  PM#1

    jinsing7 is offline
    Scoobie Regular

    P System Lean FIXED!

    Alright, so I've got the Suby ready to sell and I've even got a buyer but I've got an issue to get ironed out before handing over the keys. Change the plugs and oil about a month and a half ago and got a maf sensor error and get a P system lean code after resetting the ECU. I've been troubleshooting since then but can't seem to get the P ironed out. The cel only pops at idle and the car runs great through the power band.

    Here's what I've already done. Me and Todd swapped front O2 sensors, maf and dug everywhere for vacuum and exhaust leaks and found nothing. Had Jake check the tune and everything looked alright. ECU seems to be correcting A/F by adding 25% extra fuel to make up for the system being lean. I'm no longer getting a MAF error after cleaning it but still getting P Cleaned the IACV and MAP. I Pulled the injectors and rigged up a way to clean them externally with some sea foam and gas. No go. Found a TINY exhaust leak at one of the header cross pipe gaskets and fixed it, no go. Replaced one injector that I thought may be causing the issue and no go. I can't figure out what's going on. I wanted to have Chris at LS Subaru take a look to see if he see's anything on the Suby diagnostics but I can't seem to work out a time with him and was thinking of just taking it into the dealership to see what's going on but I don't really feel like getting bent over too bad.

    Here's the kicker, car works perfect except for at idle. Spools up perfect, pulls hard as hell but idles a little rough and pops a P CEL. Compression and leak down test was good so everything internally is solid.

    I've been reading this thread and tried just about everything I can in it
    http://forums.nasioc.com/forums/showthr ight=p

    Anyone have any ideas?? Otherwise, LSS is the next step to figure this thing out .

    -Lonnie
    AW STI - Stage 2, Cosco car seat add-on in back seat
    SOLD ** PSM WRX - EJ25 Hybrid with 18g goodness


  • ,  PM#2

    Justin 05 Sti is offline
    Super Moderator Justin 05 Sti's Avatar

    Re: P System Lean DAMN Gremlin in the system

    Lonnie I have to say you're a very thoughtful seller, most would just play dumb or disable the code to sell it.

    If the front O2 is known good, it almost has to be a vacuum leak.

    Have you hooked up a vacuum gauge to actually see what it's pulling at idle?

    Can you rig up a pressure tester and maybe find it that way?

    Is your brake booster rusty?


  • ,  PM#3

    jinsing7 is offline
    Scoobie Regular

    Re: P System Lean DAMN Gremlin in the system

    I know the buyer, plus I'd hate for someone to do it to me. I've gotta keep my good karma .

    My boost guage reads vacuum at idle. It fluctuates between the 14 and 16 during the little stutters. I haven't actually made a tester or anything.

    Brake booster was on my list but I don't think I ever actually checked it out. Thanks Justin!

    -Lonnie
    AW STI - Stage 2, Cosco car seat add-on in back seat
    SOLD ** PSM WRX - EJ25 Hybrid with 18g goodness


  • ,  PM#4

    Justin 05 Sti is offline
    Super Moderator Justin 05 Sti's Avatar

    Re: P System Lean DAMN Gremlin in the system

    Have you logged the front O2 to see what it's reporting? It could be the sensor is fine but the plug or wiring harness is fubar.

    Along those lines, if you would like to borrow my wideband for testing just let me know.


  • ,  PM#5

    jinsing7 is offline
    Scoobie Regular

    Re: P System Lean DAMN Gremlin in the system

    I'd love to borrow it and see what she's actually reading. Jake's wideband is broken. Let me know when we can meet up.

    -Lonnie
    AW STI - Stage 2, Cosco car seat add-on in back seat
    SOLD ** PSM WRX - EJ25 Hybrid with 18g goodness


  • ,  PM#6

    Justin 05 Sti is offline
    Super Moderator Justin 05 Sti's Avatar

    Re: P System Lean DAMN Gremlin in the system

    I sent ya a PM.

  • ,  PM#7

    BigC is offline
    Scoobie Expert BigC's Avatar

    Re: P System Lean DAMN Gremlin in the system

    Lonnie, I have a vaccuum gauge we could hook up to double check your boost gauge readings My hybrid reads hg on the boost gauge very consistently. Todd has said more than once that my car has great vacuum at idle, lol. Yours reads a bit higher like there could be a vacuum leak somewhere

    -Brent

    '13 XV Crosstrek Premium CVT
    '11 Legacy i Premium CVT
    '01 Forester S 4EAT
    '04 BMW RR


  • ,  AM#8

    Kilby33 is offline
    Scoobie Expert Kilby33's Avatar

    Re: P System Lean DAMN Gremlin in the system

    Leaving my friends house today I had a cel come on DAMNIT IT . So I went straight home and popped the hood to see what I could find didn't see anything at first. Got the ap out checked to the code it came up P system to lean bank 1. So I cleaned the maf sensor and continued to check it out. I found the hose clamp on the air duct hose that connects the ic to the tb was really loose and the back worked its self off a little. Fixed that and cleared out the code with the ap. It went away and hasn't come back.

    Be sure to check all the hose clamps make sure there all tight. I know it's silly but it helped me out.


  • ,  PM#9

    jinsing7 is offline
    Scoobie Regular

    Re: P System Lean DAMN Gremlin in the system

    QuoteOriginally Posted by kilby33

    Be sure to check all the hose clamps make sure there all tight. I know it's silly but it helped me out.

    Checked them all visually and with the brake cleaner trick nuthin.

    -Lonnie
    AW STI - Stage 2, Cosco car seat add-on in back seat
    SOLD ** PSM WRX - EJ25 Hybrid with 18g goodness


  • ,  PM#10

    fishawrx is offline
    Scoobie Expert

    Re: P System Lean DAMN Gremlin in the system

    I threw an this morning under normal driving. Can't find any hoses popped off, but I have been blowing the driver's side valve cover breather hose off under boost recently. Good luck finding your gremiln


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    P + P Subaru Forester

    P and P both indicate that there is a lean condition present in your Subaru Forester.  By themselves, these are some of the most common OBD2 codes.   When they appear together, it indicates that the entire engine is running lean.

    Definition

    Both of these codes are generic, which means they have the same meaning (Forester or not).

    • P&#; Fuel Trim System Lean → Bank 1:  P indicates that the side of the engine with the first cylinder (Bank 1) is running lean. 
    • P Fuel Trim System Lean → Bank 2: P indicates that the side of the engine with the first cylinder (Bank 2) is running lean.  On inline engines, this code is not available, since there is only one &#;bank&#; of cylinders.
    • Lean Condition Meaning:  The engine is bringing in too much air to the amount of fuel present.  There are a few reasons that a vehicle will get a lean condition.  It could be getting too much air (think vacuum leak, EGR problem, or mass airflow sensor) or it is not getting enough fuel (bad injectors, weak fuel pump, dirty fuel filter, bad fuel pressure regulator).  Here&#;s more

     

    P and P occur when the air/fuel mixture on the vehicle gets too lean. They are both thrown when the oxygen sensors detect that there is not enough oxygen in the exhaust. The engine then makes adjustments to compensate and throws these codes, which trigger the service engine soon light.

    When these codes both appear at the same time, it is more often than not the intake manifold gasket that is the cause of the problem. It can be other things as well, but the intake manifold gasket is a great place to start.

    Subaru Forester P+P Diagnosis

    Symptoms:  P + P Subaru Forester

    There aren&#;t always drivability issues associated with these codes. For most people the first sign that anything is wrong at all is the service engine soon light coming on.

    Here are the typical symptoms that something is wrong when your Forester has codes P and P

    • Fuel Mileage- may or may not suffer depending on how much the air fuel mixture has changed.
    • Misfire&#; If the air fuel mixture has gotten too far from factory specs, this can cause the vehicle to misfire or run rough.  This will often be accompanied by P  If you have this code along with P and P, ignore the P  It should resolve when you get the air/fuel mixture issue fixed.
    • Idle Issues&#; With the air/fuel mixture altered, the vehicle can idle erratically as the computer compensates to keep the engine running.  The engine may sputter as well.

     

    Causes

    Here are the most common causes of P + P  Vacuum leaks (particularly at the intake manifold) and the MAF sensor are the most common culprits.

     

    Vacuum Leaks

    With most vehicles, the most common cause for the P or P code to show is a vacuum leak. Take a look around and see if you can find the vacuum leak. Here&#;s a great YouTube video on how to go about finding one.  If the engine is letting in unmetered air, the intake manifold leaking is a very high likelihood.  But, the leak can be anywhere.

    A good scan tool can help you determine if there is a vacuum leak as well.  Fuel trim at idle will be greatly affected by a vacuum leak.  But, as you rev the engine, the fuel trim should dip down to around 0 (give or take a few points).

     

    Mass Air Flow Sensor

    The mass air flow sensor calculates the volume of air entering the engine. If it has gone bad, the air fuel mixture will be off and the P and/or P codes will show.  It&#;ll be located between the air filter and the throttle body.  It&#;s easy to find.  It will have a wiring harness plugged into it.

    The number one culprit when it comes to the MAF sensor going bad is dirty air.  This typically happens when the air filter has a bad seal.  It&#;ll let unfiltered air in and it can quickly get the MAF sensor dirty enough that it will no longer work properly.  Another way they can stop working properly is if they get dirty from fuel vapor.

    Either way, the mover here is to clean it with a MAF sensor cleaner.  Don&#;t use anything else.  It&#;s very sensitive.  If it&#;s still not working, you may need to get a new one.  Subaru Forester: Bad MAF Sensor

    Typical MAF Sensor Location

     

    EGR

    The EGR system is designed to recycle exhaust gasses for cleaner emissions.  If it has gone bad, you may get these codes as it throws off your Forester&#;s vacuum level.

     

    Bad Fuel Injectors

    If you have one or more fuel injectors that have gone bad that can certainly cause the air/fuel mixture to go bad.  But, P and P indicate that BOTH sides of the engine are running lean.  One bad fuel injector would cause one of those codes to show up.  Multiple fuel injectors going bad on both sides of the engine could cause both codes to show, but it&#;s unlikely.

    If you have more than one cylinder related misfire codes (such as PX, where X is the misfiring cylinder) then it may be possible that you have more than one bad injector.  Bad Fuel Injector Diagnosis

     

    Fuel Pump/Fuel Filter

    Today&#;s modern fuel injected motors need a lot of fuel pressure to atomize the gas properly. If the fuel pressure is not as high as it needs to be this atomization doesn&#;t happen properly and the optimal air/fuel mixture isn&#;t achieved.  This is common when the fuel pump is bad, or the fuel filter is clogged.  The fuel pressure regulator can also be the culprit.  There&#;s more than likely a port you can use to check the fuel pressure.  Do that before anything else.

    Here&#;s a great YouTube video on the subject. This guy really gets into the problem, and can really help you find the cause of the code.

     

    Conclusion

    Good luck figuring out what is causing the P and P trouble codes with your Subaru Forester.  If you feel like you could improve this article in any way, please feel free to leave a comment below. 

    Categories Subaru ForesterSours: https://wwwr4transmissionhq.com/subaru-forester-pp/
    P0171 System Too Lean Bank 1 - How to Fix Car Hesitation -

    P SUBARU Code - System Too Lean Bank 1

    AutoCodes - Subaru - P SUBARU

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    What does this mean?

    &#;P SUBARU code possible causes

    • Intake air leaks
    • Faulty front heated oxygen sensor
    • Ignition misfiring
    • Faulty fuel injectors
    • Exhaust gas leaks
    • Incorrect fuel pressure
    • Lack of fuel
    • Faulty Mass Air Flow (MAF) sensor
    • Incorrect Positive Crankcase Ventilation (PCV) hose connection

    &#;How do I fix the P SUBARU code?

    Check the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

    What does this mean?

    &#;P SUBARU code tech notes

    If the P is combined with the P code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replace the air filter and clean the air flow meter. If the problem persists the front oxygen (O2) sensor may need to be replaced.

    &#;Cost of diagnosing the P SUBARU code

    Labor:

    The cost of diagnosing the P SUBARU code is hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $ per hour.

    &#;When is the P SUBARU code detected?

    - Fuel injection system does not operate properly
    - The amount of mixture ratio compensation is too small. (The mixture ratio is too lean.)

    &#;What are P SUBARU code possible symptoms?

    • Engine Light ON (or Service Engine Soon Warning Light)
    • Excessive Fuel Consumption

    &#;P SUBARU code description

    With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The Engine Control Module (ECM) calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.
    In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the ECMjudges the condition as the fuel injection system malfunction and light up the MIL (2 trip detection logic).
    OBDII Code P Subaru - System Too Lean Bank 1 - AutoCodes.com

    &#;Need more information with the P SUBARU code?

    Need more information on how to fix the P SUBARU code?
    Get Access to Factory Service Manuals

    &#;P SUBARU code comments

    Help us improve AutoCodes.com. Leave a comment below or tell us if the information above helps you fix the code. What are the symptoms on your vehicle for the P Subaru code? Have you replaced any parts?
    Any information is appreciated. Thanks

    Top &#;

    Repair Importance Level:3

     

    1=Low 2=Medium 3=High What is this?

    Repair Difficulty Level:3

     

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    Code forester p0171 subaru

    P SUBARU Code - System Too Lean Bank 1

    Engine-Codes - Subaru - P SUBARU

    Repair Importance Level: 3/3

    Repair Difficulty Level: 3/3  What is this?

    What does this mean?

    &#;P SUBARU code possible causes

    • Intake air leaks
    • Faulty front heated oxygen sensor
    • Ignition misfiring
    • Faulty fuel injectors
    • Exhaust gas leaks
    • Incorrect fuel pressure
    • Lack of fuel
    • Faulty Mass Air Flow (MAF) sensor
    • Incorrect Positive Crankcase Ventilation (PCV) hose connection

    &#;How is the P SUBARU code repair?

    Start by checking the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.

    What does this mean?

    &#;P SUBARU code tech notes

    If the P is combined with the P code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replace the air filter and clean the air flow meter. If the problem persists the front oxygen (O2) sensor may need to be replaced.

    &#;What is the cost to diagnose the P SUBARU code

    Labor:

    The cost to diagnose the P SUBARU code is hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $ per hour.

    &#;When is the P SUBARU code detected?

    - Fuel injection system does not operate properly
    - The amount of mixture ratio compensation is too small. (The mixture ratio is too lean.)

    &#;What are P SUBARU code possible symptoms?

    • Engine Light ON (or Service Engine Soon Warning Light)
    • Excessive Fuel Consumption

    &#;What is P SUBARU code meaning?

    With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The Engine Control Module (ECM) calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.
    In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the ECMjudges the condition as the fuel injection system malfunction and light up the MIL (2 trip detection logic).

    &#;Need more information with the P SUBARU code?

    Need more information on how to fix the P SUBARU code?
    Get Access to Factory Service Manuals

    Repair Importance Level:3

     

    1=Low 2=Medium 3=High What is this?

    Repair Difficulty Level:3

     

    1=Easy 2=Moderate 3=Hard What is this?

    Browse Codes for Specific Model-Year

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    Cleaning the Mass Airflow Sensor in a Subaru 2.5i Legacy or Outback

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