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Subaru · Fuel System · Moderate code

P0171 on Subaru: How to Diagnose & Fix

System Too Lean (Bank 1)

8 Subaru models · 14 documented issues · 9 critical · $1,200-$10,000 repair

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P0171 by Subaru model

  • 1999-2019Outback3
  • 1999-2011Impreza1
  • 2000-2016Legacy2
  • 2011-2020Forester2
  • 2015-2021WRX3
  • 2013-2017Crosstrek1
  • 2003-2006Baja1
  • 2019-2022Ascent1
  • FAQ

P0171 on other makes

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  • Audi
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P0171 by Subaru model

  • 1999-2019Outback3
  • 1999-2011Impreza1
  • 2000-2016Legacy2
  • 2011-2020Forester2
  • 2015-2021WRX3
  • 2013-2017Crosstrek1
  • 2003-2006Baja1
  • 2019-2022Ascent1
  • FAQ

P0171 on Subaru by model: symptoms, diagnosis and fix

Community reported
4,521 owners
Link to this issueError Codes:P0171P0174P0300P0301P0302P0303P0304P0128

The 2.5L non-turbo engine is known for external head gasket leaks. Oil seeps past the gasket and can contaminate the coolant. Subaru extended warranties and improved gasket design in later years.

Common Symptoms

  • Oil leaking externally from engine
  • Coolant mixing with oil (milky appearance)
  • Overheating
  • Sweet smell from engine bay
  • Bubbles in coolant reservoir

How to Fix

Replace head gaskets with updated MLS (multi-layer steel) gaskets. Ensure the machine shop resurfaces cylinder heads to proper flatness. Replace timing belt, water pump, and thermostat while engine is apart. Use Subaru coolant conditioner to help prevent future failures. Budget $1,500-2,500 for a quality repair.

What you need to fix it

Only diagnosis- and fitment-reviewed repair parts are linked here.

  • Genuine Subaru 11044AA610 EJ25D Cylinder-Head Gasket

    head gasket for each bank on the 1999 2.5-liter branch after failure is confirmed Fitment/availability: 1999 Outback 2.5-liter EJ25D DOHC branch; quantity two, confirm VIN Fitment/availability: ships in 1-3 business days with Add to Cart…

    SubaruPartsDeal
  • Genuine Subaru 11044AA633 SOHC Cylinder-Head Gasket

    head gasket for each bank on the 2000-2009 naturally aspirated branch Fitment/availability: 2000-2009 Outback naturally aspirated 2.5-liter branch; quantity two, confirm VIN and exclude turbo Fitment/availability: ships in 1-3 business d…

    SubaruPartsDeal
  • Genuine Subaru 11044AA770 Cylinder-Head Gasket

    head gasket for each bank on the 2010 branch Fitment/availability: 2010 Outback naturally aspirated 2.5-liter EJ253 branch via supersession from 11044AA670; quantity two, confirm VIN Fitment/availability: ships in 1-3 business days with …

    SubaruPartsDeal
  • Genuine Subaru 13028AA072 EJ25D Timing Belt

    timing belt when removed, due or of unknown history on the 1999 branch Fitment/availability: 1999 Outback 2.5-liter EJ25D DOHC branch; confirm VIN Fitment/availability: ships in 1-2 business days with Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 13028AA21B SOHC Timing Belt

    timing belt when removed, due or of unknown history on the 2000-2009 branch Fitment/availability: 2000-2009 Outback naturally aspirated 2.5-liter branch; confirm VIN Fitment/availability: ships in 1-3 business days with Add to Cart live …

    SubaruPartsDeal
  • Genuine Subaru 13028AA231 Timing Belt

    timing belt when removed, due or of unknown history on the 2010 branch Fitment/availability: 2010 Outback naturally aspirated 2.5-liter EJ253 branch; confirm VIN and production date Fitment/availability: ships in 1-3 business days with A…

    SubaruPartsDeal
  • Genuine Subaru 13033AA042 Hydraulic Timing-Belt Tensioner

    tensioner renewed with a due or unknown-history complete timing service Fitment/availability: 1999-2010 Outback 2.5-liter timing-belt branches in this card; confirm VIN and configuration Fitment/availability: ships in 1-3 business days w…

    SubaruPartsDeal
  • Genuine Subaru 21111AA110 Water Pump

    early water pump only when failed, leaking, rough, due or selected for unknown-history service Fitment/availability: 1999-2005 Outback 2.5-liter branch within this card; confirm VIN and required seal Fitment/availability: ships in 1-2 bu…

    SubaruPartsDeal
  • Genuine Subaru 21111AA280 Water Pump

    middle-year water pump when condition or service history warrants replacement Fitment/availability: 2006-2009 Outback naturally aspirated 2.5-liter branch; confirm VIN Fitment/availability: ships in 1-3 business days with Add to Cart liv…

    SubaruPartsDeal
  • Genuine Subaru 21111AA320 Water Pump

    2010 water pump when condition or service history warrants replacement Fitment/availability: 2010 Outback naturally aspirated 2.5-liter branch; confirm VIN Fitment/availability: ships in 1-3 business days with Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 21210AA030 Thermostat and Gasket Assembly

    thermostat only when diagnosis or condition warrants replacement on the 2000-2009 branch Fitment/availability: 2000-2009 Outback 2.5-liter branch; the 1999 branch requires VIN-specific selection Fitment/availability: Add to Cart live whe…

    SubaruPartsDeal
  • Genuine Subaru 21210AA080 Thermostat and Gasket Assembly

    2010 thermostat only when diagnosis or condition warrants replacement Fitment/availability: 2010 Outback naturally aspirated 2.5-liter branch; confirm VIN Fitment/availability: ships in 1-3 business days with Add to Cart live when reviewed

    SubaruPartsDeal

As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.

Owner tips & cautions

  • TipDIY repairs can save significantly - dealer charges $1,500-2,500 but DIY costs are typically 50-70% less
  • TipUse Subaru coolant conditioner to help prevent future failures.
  • WarningThis is a high-severity issue - ignoring it can lead to costly repairs or safety concerns. Address it promptly.
  • TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
Typical repair cost:$1,500 - $2,500
Sources for this issue (4)
  • Head Gasket Failure in 2.2 liter models - Subaru Outback Forumsforum
  • Subaru Head Gasket Problems Explained - All Wheel Drive Automedia
  • Ej25 sohc 2000 ob head gasket - Ultimate Subaruforum
  • Subaru Head Gasket Problems Crucial Years - Automotive Body Caremedia

Research This Issue

Based on 4,521 owner reports

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Community Reported
High ConfidenceVerified4,521 owner reportsLast reported by owners Jan 2024Reviewed Feb 2026
Community reported
2,800 owners
Link to this issueError Codes:P0420P0171P0174

The FB25 2.5L engine is known for excessive oil consumption, sometimes using 1 quart every 1,000-2,000 miles. Subaru extended warranty coverage and offered piston ring replacement for affected vehicles. Most common on 2011-2014 models.

Common Symptoms

  • Need to add oil between changes
  • Low oil warning light
  • Blue smoke from exhaust
  • Oil level drops quickly
  • Burning oil smell

How to Fix

Monitor oil level frequently. Check if covered by Subaru oil consumption warranty extension. If consumption test confirms issue, piston ring replacement may be covered. Use Subaru-recommended oil.

Owner tips & cautions

  • TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
  • TipSearch Subaru Outback forums and owner groups for real-world experiences and DIY guides
  • TipGet multiple quotes from independent mechanics - dealer prices can be 2-3x higher for the same repair
Typical repair cost:$0 - $4,000

Research This Issue

Based on 2,800 owner reports

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Community Reported
High Confidence2,800 owner reportsLast reported by owners Jun 2022Reviewed Feb 2026
Community reported
680 owners
Link to this issueError Codes:P0171P0174P0300P0301P0302P0303P0304P0128

While the FB25 has improved head gasket reliability compared to older EJ engines, some vehicles still experience head gasket failures. External oil leaks and coolant leaks can develop, particularly at higher mileage.

Common Symptoms

  • Oil leak near head gasket
  • External coolant leak
  • Overheating
  • Sweet coolant smell
  • Oil mixing with coolant (rare)

How to Fix

Monitor for coolant and oil leaks around head gasket area. Replace head gaskets if leaking. Use proper Subaru coolant. This is less common than on older EJ engines but still occurs.

Owner tips & cautions

  • TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
  • TipSearch Subaru Outback forums and owner groups for real-world experiences and DIY guides
  • TipGet multiple quotes from independent mechanics - dealer prices can be 2-3x higher for the same repair
Typical repair cost:$1,200 - $2,500
Sources for this issue (1)
  • Subaru-Forums.com thread discussing FB25 head gasket failuresforum

Research This Issue

Based on 680 owner reports

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Community Reported
Medium Confidence680 owner reportsLast reported by owners Feb 2023Reviewed Feb 2026
All Subaru Outback known issues →
Community reported
4,200 owners
Link to this issueError Codes:P0171P0174P0300P0301P0302P0303P0304P0128

The 2.5L EJ253 naturally-aspirated engine in 1999-2011 Imprezas is notorious for external head gasket failure. The composite head gaskets degrade over time, allowing coolant and oil to seep externally at the gasket mating surfaces. Unlike a typical blown head gasket that causes coolant-oil mixing, Subaru EJ25 head gaskets typically leak externally first. The boxer engine design means gaskets are at the bottom of the heads, making leaks drip downward and often go unnoticed. If left unaddressed, external leaks can progress to internal coolant-oil mixing and overheating.

Common Symptoms

  • Oil seepage visible on bottom of engine near head gasket area
  • Coolant level slowly dropping without visible external puddles
  • Sweet coolant smell from engine bay
  • Oil spots on garage floor near front of vehicle
  • Overheating in severe cases (internal gasket breach)
  • Bubbles in coolant overflow reservoir

How to Fix

Replace both head gaskets with updated MLS (multi-layer steel) gaskets (Subaru OEM 11044AA770 or Six Star MLS set). Resurface both cylinder heads to within 0.002 inch flatness spec. Replace timing belt, water pump (21111AA370), thermostat, and all seals while the engine is apart. Add Subaru Cooling System Conditioner (SOA635071) after repair. Budget 8-12 hours labor for the complete job.

What you need to fix it

Only diagnosis- and fitment-reviewed repair parts are linked here.

  • Genuine Subaru 11044AA633 Naturally Aspirated Head Gasket

    current OE MLS head gasket after the affected engine and failure are confirmed Fitment/availability: 1999-2011 naturally aspirated 2.5-liter Impreza EJ251/EJ253 applications; quantity two, confirm VIN and engine Fitment/availability: Add…

    Subaru Online Parts
  • Genuine Subaru 21111AA007 Water Pump

    water pump only when failed, contaminated or due during accessible timing service Fitment/availability: 1999-2005 naturally aspirated 2.5-liter Impreza branch within this issue; confirm VIN and engine Fitment/availability: ships in 1-3 b…

    SubaruPartsDeal
  • Genuine Subaru 21111AA280 Water Pump

    later-branch water pump only when failed, contaminated or due during accessible timing service Fitment/availability: 2006-2011 naturally aspirated 2.5-liter Impreza branch within this issue; confirm VIN and engine Fitment/availability: A…

    Subaru Parts Guys
  • Genuine Subaru 21200AA072 Thermostat Assembly

    thermostat when testing, age or contamination warrants replacement Fitment/availability: Use here for the confirmed 1999-2005 naturally aspirated Impreza branch; verify VIN and catalog split Fitment/availability: ships in 1-3 business da…

    SubaruPartsDeal
  • Genuine Subaru 21200AA170 Thermostat Assembly

    later-branch thermostat when testing, age or contamination warrants replacement Fitment/availability: 2006-2011 naturally aspirated 2.5-liter Impreza branch within this issue; confirm VIN and engine Fitment/availability: ships in 1-3 bus…

    SubaruPartsDeal

As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.

Typical repair cost:$1,500 - $2,800
Sources for this issue (4)
  • Subaru Head Gasket Problems Explained - All Wheel Drive Automedia
  • EJ251 Head Gasket Problems - RS25forum
  • Head Gasket Problems Explained - RS25forum
  • Head gasket problem fixed in 2001 2.5 RS - RS25forum

Research This Issue

Based on 4,200 owner reports

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Community Reported
High Confidence4,200 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
All Subaru Impreza known issues →
Community reported
3,800 owners
Link to this issueError Codes:P0171P0174P0300P0301P0302P0303P0304P0128

The 2.5L EJ25 engine in 2000-2009 Legacys suffers from the same head gasket failure that plagues all EJ25-equipped Subarus. The composite gaskets degrade, causing external oil and coolant leaks at the head-to-block mating surfaces. The Legacy's higher-mileage highway use means many owners encounter this between 80,000-150,000 miles. Phase 1 engines (2000-2005, single overhead cam) are more prone to coolant leaks, while Phase 2 engines (2006-2009, DOHC) tend to leak oil externally first.

Common Symptoms

  • External oil seepage at bottom of cylinder heads
  • Coolant level gradually decreasing
  • Oil and coolant mixing (milky residue on oil cap)
  • Overheating at highway speeds
  • Sweet smell from engine compartment
  • White exhaust smoke in severe cases

How to Fix

Replace both head gaskets with updated MLS (multi-layer steel) gaskets. Use Six Star MLS gasket kit or Subaru OEM MLS (11044AA633 for SOHC, 11044AA770 for DOHC). Machine heads to 0.002-inch flatness. Replace timing belt, tensioner, idlers, water pump, thermostat, and valve cover gaskets while apart. Use Subaru Cooling System Conditioner (SOA635071). Total job is 10-14 hours labor.

What you need to fix it

Only diagnosis- and fitment-reviewed repair parts are linked here.

  • Genuine Subaru 11044AA633 SOHC Cylinder-Head Gasket

    OE head gasket for each bank after failure is confirmed on the naturally aspirated branch Fitment/availability: 2000-2009 Legacy naturally aspirated 2.5-liter SOHC branch; quantity two, confirm VIN and exclude turbo GT Fitment/availabili…

    SubaruPartsDeal
  • Genuine Subaru 11044AA642 Turbo Cylinder-Head Gasket

    OE head gasket for each bank on the early Legacy GT turbo branch Fitment/availability: 2005-2006 Legacy GT and GT Limited 2.5-liter turbo branch; quantity two, not for the naturally aspirated engine Fitment/availability: ships in 1-3 bus…

    SubaruPartsDeal
  • Genuine Subaru 11044AA770 Turbo Cylinder-Head Gasket

    OE head gasket for each bank on the later Legacy GT turbo branch Fitment/availability: 2007-2009 Legacy GT and GT Limited 2.5-liter turbo branch; quantity two, confirm VIN and production date Fitment/availability: direct Add to Cart prod…

    SubaruPartsDeal
  • Genuine Subaru 13028AA21B Naturally Aspirated Timing Belt

    timing belt when removed, due or of unknown history during the naturally aspirated repair Fitment/availability: 2000-2009 Legacy naturally aspirated 2.5-liter SOHC branch; confirm VIN Fitment/availability: ships in 1-3 business days with…

    SubaruPartsDeal
  • Genuine Subaru 13028AA240 Turbo Timing Belt

    timing belt when removed, due or of unknown history during the turbo repair Fitment/availability: 2005-2009 Legacy GT 2.5-liter turbo branch within this card; retailer catalogs the broader 2004-2012 turbo range, so confirm VIN Fitment/av…

    SubaruPartsDeal
  • Genuine Subaru 21111AA110 Naturally Aspirated Water Pump

    water pump when failed, leaking, rough, due or selected for an unknown-history full timing service Fitment/availability: 2000-2005 Legacy naturally aspirated 2.5-liter branch; confirm VIN and required gasket/seal Fitment/availability: sh…

    SubaruPartsDeal
  • Genuine Subaru 21111AA280 Naturally Aspirated Water Pump

    later naturally aspirated water pump when condition or service history warrants replacement Fitment/availability: 2006-2009 Legacy naturally aspirated 2.5-liter branch; confirm VIN and production split Fitment/availability: direct Add to…

    SubaruPartsDeal
  • Genuine Subaru 21111AA240 Turbo Water Pump

    turbo water pump when failed, leaking, rough, due or selected for a full timing service Fitment/availability: 2005-2009 Legacy GT 2.5-liter turbo branch within this card; confirm VIN and required gasket/seal Fitment/availability: ships i…

    SubaruPartsDeal
  • Genuine Subaru 13033AA042 Hydraulic Timing-Belt Tensioner

    hydraulic tensioner renewed with a complete due or unknown-history timing service Fitment/availability: 2000-2009 Legacy 2.5-liter timing-belt branches in this card; confirm VIN, engine and production configuration Fitment/availability: …

    SubaruPartsDeal
  • Genuine Subaru 13073AA142 Timing-Belt Idler

    smooth timing idler in the exact engine-specific position and quantity Fitment/availability: 2000-2009 Legacy 2.5-liter timing applications; position and quantity vary, so confirm VIN and engine diagram Fitment/availability: ships in 1-3…

    SubaruPartsDeal
  • Genuine Subaru 13085AA080 Timing-Belt No. 2 Idler

    2 timing idler for the exact engine-specific timing layout Fitment/availability: 2000-2009 Legacy 2.5-liter timing applications; confirm VIN, engine, position and quantity Fitment/availability: ships in 1-3 business days with Add to Cart…

    SubaruPartsDeal

As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.

Typical repair cost:$1,600 - $3,000
Sources for this issue (5)
  • All Wheel Drive Auto: Subaru Head Gasket Problems Explainedmedia
  • Jalopnik: These Subaru Model Years Were The Worst Affected By Head Gasket Problemsmedia
  • Fel-Pro: Solving Subaru 2.5L Head Gasket Problemsmanufacturer
  • HiRide: Subaru Outback Head Gasket Leak Symptoms Causes & DIY Diagnosismedia
  • Subimods: How to Spot a Blown Head Gasket in Your Subarumedia

Research This Issue

Based on 3,800 owner reports

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Community Reported
High Confidence3,800 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
Community reported
870 owners
Link to this issueError Codes:P0420P0171P0174

The 2010-2016 Legacy 2.5i uses the FB25 engine which is affected by the same oil consumption issue as other FB25-equipped Subarus. Defective piston rings allow excessive oil to bypass into the combustion chamber. The Legacy's higher average speeds mean oil consumption can be even more noticeable during highway driving. Subaru's oil consumption warranty extension and the Oakes v. Subaru settlement cover affected vehicles.

Common Symptoms

  • Oil level drops 1+ quart between oil changes
  • Low oil warning light
  • Blue smoke from exhaust, particularly on cold start
  • Oil fouling spark plugs causing misfires
  • Catalytic converter premature failure (P0420 code)

How to Fix

Have dealer perform official oil consumption test (OCT). If consumption exceeds 1 qt per 3,000 miles, piston ring replacement or short block replacement is warranted. Check coverage under Subaru powertrain warranty extension (8 years/100,000 miles) or Oakes v. Subaru settlement. Use 0W-20 full synthetic oil and monitor levels weekly.

Typical repair cost:$0 - $4,500
Sources for this issue (4)
  • Jalopnik: Subaru Owners Win Compensation And Warranty Boost For Oil-Burning Carsmedia
  • Subaru Outback Forums: Subaru Settles Oil Consumption Lawsuitforum
  • Subaru Forester Owners: 2011+ FB25 discussion about oil consumptionforum
  • Subaru Outback Forums: Lawsuit charges Subaru engines may have defective piston ringforum

Research This Issue

Based on 870 owner reports

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Community Reported
High Confidence870 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
All Subaru Legacy known issues →
Community reported
3,200 owners
Link to this issueError Codes:P0420P0171P0174

The 2.5L FB25 engine in 2011-2018 Foresters is widely reported for excessive oil consumption, often burning 1 quart every 1,000-1,500 miles. The root cause is defective piston rings that fail to maintain proper oil control. Subaru acknowledged the issue with TSB 02-157-14R and extended the powertrain warranty to 8 years/100,000 miles for affected vehicles. A class-action settlement (Oakes v. Subaru) covered ring replacement for qualifying owners. The oil consumption test (OCT) required by Subaru involves monitoring oil usage over 3,000 miles at the dealership.

Common Symptoms

  • Oil level drops significantly between changes
  • Low oil pressure warning light
  • Blue or grey smoke from exhaust on startup
  • Need to add 1+ quart of oil every 1,000-1,500 miles
  • Burning oil smell from engine bay

How to Fix

Request an oil consumption test (OCT) at a Subaru dealer. If consumption exceeds 1 qt per 3,000 miles, piston ring replacement is warranted. The fix involves replacing all piston rings and sometimes pistons (Subaru part 12006-AB270 short block assembly for severe cases). Check warranty extension and class-action settlement eligibility. Use Subaru 0W-20 synthetic oil and change at 3,000-mile intervals while monitoring.

What you need to fix it

Only diagnosis- and fitment-reviewed repair parts are linked here.

  • Genuine Subaru SOA427V1310 Synthetic 0W-20 Engine Oil, 1 Quart

    maintaining the safe level and performing a controlled consumption test, not repairing worn rings Fitment/availability: Top-off or controlled-test fluid only where the exact Forester owner's manual and test procedure call for 0W-20; conf…

    Oakos Automotive

As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.

Typical repair cost:$0 - $4,500
Sources for this issue (4)
  • Is Your Subaru Burning Oil - A&A The Shopmedia
  • 2012 Replacement engine Subaru oil consumption - Subaru Forester Ownersforum
  • 2011+ FB25 oil consumption discussion - Subaru Forester Ownersforum
  • The 3 Most Common Subaru FB25 Engine Problems - 8020 Automotivemedia

Research This Issue

Based on 3,200 owner reports

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Community Reported
High Confidence3,200 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
Link to this issueError Codes:P0087P0171

Foresters equipped with a Denso low-pressure fuel pump (part-number prefix 42022-) built before mid-2019 use a low-density plastic impeller that absorbs fuel, swells and deforms inside the pump housing. The deformed impeller binds against the housing and abruptly cuts fuel delivery, causing the engine to hesitate, run rough, fail to start, or stall without warning while driving — a crash risk. The defect is covered by NHTSA recall 21V-587 (one of several Subaru/Denso fuel-pump campaigns) and a class-action settlement that extended the pump warranty to 15 years/150,000 miles on replaced units.

Common Symptoms

  • Sudden engine stalling while driving
  • Long crank / no-start, especially when warm
  • Hesitation and surging under acceleration
  • Rough running and rough idle
  • Whining or no priming sound from the tank

How to Fix

Have the VIN checked for the open fuel-pump recall and get the complete in-tank fuel pump assembly (Denso, 42022- prefix) replaced free under the recall — the new assembly uses a higher-density impeller that resists swelling. Out of warranty, replace the entire module (pump, sender, filter sock) rather than just the impeller; budget for intermittent stalling diagnosis since the failure can be load/temperature dependent and may not store a code.

Typical repair cost:$0 - $1,300
Sources for this issue (3)
  • NHTSA Part 573 Safety Recall Report 21V-587 (Subaru Denso fuel pump)nhtsa
  • Subaru Recalls More Than 165,000 Cars and SUVs to Fix Stalling Engines — Consumer Reportsarticle
  • Fuel Pump Recall for 2018 Forester XT — Subaru Forester Owners Forumforum

Research This Issue

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Community Reported
Medium ConfidenceVerifiedReviewed Jun 2026
All Subaru Forester known issues →
Community reported
1,050 owners
Link to this issueError Codes:P0171P0174P052E

The FA20DIT engine can consume oil at a rate higher than expected, sometimes up to 1 quart every 1,000-3,000 miles. This is often related to the turbocharger, PCV system, or piston ring design. Subaru considers up to 1 quart per 1,200 miles as within normal range.

Common Symptoms

  • Oil level drops between changes
  • Need to add oil between scheduled changes
  • Light blue smoke at startup or deceleration
  • Oil residue around turbo
  • Low oil pressure warnings

How to Fix

Check oil level frequently (every fuel fill-up). Use high-quality synthetic oil that meets Subaru specifications. Inspect PCV system for proper operation. Monitor for turbo seal leaks. If consumption is excessive, oil consumption test at dealer may warrant warranty coverage.

Owner tips & cautions

  • TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
  • TipSearch Subaru WRX forums and owner groups for real-world experiences and DIY guides
  • TipGet multiple quotes from independent mechanics - dealer prices can be 2-3x higher for the same repair
Typical repair cost:$0 - $3,000

Research This Issue

Based on 1,050 owner reports

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Community Reported
High Confidence1,050 owner reportsLast reported by owners Feb 2024Reviewed Feb 2026
Community reported
890 owners
Link to this issueError Codes:P0171P0174P0420

The FA20DIT engine can suffer from piston ringland failure, especially when tuned or running high boost. The ringland (area between piston rings) can crack, causing compression loss and engine damage. This is often related to detonation from improper tuning or low octane fuel.

Common Symptoms

  • Loss of power
  • Excessive oil consumption
  • Blue smoke from exhaust
  • Knocking or pinging under load
  • Compression loss on cylinder test
  • Check engine light with misfire codes

How to Fix

Always use 93 octane fuel. If tuning, use a reputable tuner with proper air/fuel ratios and timing. Consider forged pistons if building engine. Monitor for knock with an accessport or similar device. Catch early signs through oil analysis showing elevated metals.

Owner tips & cautions

  • WarningThis is a high-severity issue - ignoring it can lead to costly repairs or safety concerns. Address it promptly.
  • TipGet a proper diagnosis before replacing parts - similar symptoms can have different causes
Typical repair cost:$4,000 - $10,000

Research This Issue

Based on 890 owner reports

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Community Reported
High Confidence890 owner reportsLast reported by owners Feb 2024Reviewed Feb 2026
Link to this issueError Codes:P0171

A supplier used the wrong material for a lot of turbocharger air intake ducts fitted to 2015-2016 WRX built April 10 through October 21, 2015 (and 2016 Forester 2.0XT). The duct can crack, letting unmetered air past the MAF sensor; the FA20DIT then runs lean, idles roughly, loses power and can stall. Subaru issued a stop-sale and NHTSA recall 16V-162 (Subaru campaign WTA-62) covering 18,187 vehicles. Owners of unaffected-lot ducts still see cracked intake ducts at higher mileage, so the symptom set is worth checking even on cars outside the recall.

Common Symptoms

  • Rough idle
  • Reduced power
  • Engine stall at idle or low speed
  • Check engine light for lean condition

How to Fix

Dealer inspects the duct lot number and replaces the turbocharger air intake duct free of charge under recall 16V-162. Outside the recall population, replace a cracked duct with the current-revision OEM part or an aftermarket silicone inlet.

Find a Subaru dealer

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Call to confirm they service Subaru vehicles and check your VIN, recall eligibility, parts availability, and appointment options.

Typical repair cost:$0 - $250
Sources for this issue (3)
  • Part 573 Safety Recall Report 16V-162article
  • Repair Procedure for Subaru Recall Campaign Stop-Sale: WTA-62 Turbocharger Air Intake - subaruforester.orgforum
  • Recall Alert: 2015-16 Subaru WRX, Forester - Cars.comarticle

Research This Issue

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Community Reported
High ConfidenceVerifiedReviewed Sep 2026
All Subaru WRX known issues →
Community reported
950 owners
Link to this issueError Codes:P0420P0171P0174

The 2.0L FB20 engine in first-generation Crosstreks (2013-2017) shares the same oil consumption defect as the FB25 used in other Subaru models. Defective piston rings fail to maintain proper oil control, leading to oil burning at rates of 1 quart every 1,500-2,500 miles. Subaru covered this under warranty extension and the Oakes v. Subaru class-action settlement. The issue is most prevalent in 2013-2015 models.

Common Symptoms

  • Oil level drops 1+ quart between oil changes
  • Low oil pressure warning light illumination
  • Blue-grey exhaust smoke especially on cold start
  • Fouled spark plugs from oil contamination
  • Catalytic converter failure from excess oil burning (P0420)

How to Fix

Perform Subaru's official oil consumption test (OCT) at a dealership. If consumption exceeds 1 qt per 3,000 miles, piston ring replacement is the fix. Check coverage under the Oakes v. Subaru settlement or Subaru's powertrain warranty extension. Short block replacement (Subaru 10103AB830) may be offered for severe cases. Monitor oil level weekly and keep records of oil additions.

Find a Subaru dealer

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Call to confirm they service Subaru vehicles and check your VIN, recall eligibility, parts availability, and appointment options.

What you need to fix it

Only diagnosis- and fitment-reviewed repair parts are linked here.

  • Genuine Subaru SOA427V1310 Synthetic 0W-20 Engine Oil - 1 Quart

    maintain the exact safe oil level during diagnosis; not a cure for oil consumption Fitment/availability: Top-off and controlled-test supply only for a 2013-2017 FB20 Crosstrek whose current owner manual/service information specifies 0W-2…

    OAKOS Automotive

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Typical repair cost:$0 - $4,000
Sources for this issue (4)
  • Is Your Subaru Burning Oil - A&A The Shopmedia
  • Subaru Engines Models Years Burn Oil - Torque Newsmedia
  • FB20 Engine Tear Down repair for oil consumption - Subaru Crosstrek Forumsforum
  • Oil Consumption Problem - Subaru Crosstrek Forumsforum

Research This Issue

Based on 950 owner reports

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Community Reported
High Confidence950 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
All Subaru Crosstrek known issues →
Community reported
890 owners
Link to this issueError Codes:P0171P0174P0300P0301P0302P0303P0304P0128

The Subaru Baja's 2.5L EJ25 naturally-aspirated engine suffers from the same chronic head gasket failure that affects all EJ25-equipped Subarus. The composite gaskets degrade over time, typically between 80,000-150,000 miles, causing external oil and coolant leaks. The Baja's engine placement and bed-over-engine design can make leaks harder to spot until they become severe. The issue affects all 2003-2006 NA Bajas. Turbo models use a different gasket design and are less susceptible.

Common Symptoms

  • Oil seepage at the base of cylinder heads
  • Coolant level slowly dropping
  • Overheating at highway speeds
  • Sweet coolant smell from engine compartment
  • Milky residue on oil filler cap
  • Bubbles in coolant reservoir

How to Fix

Replace both head gaskets with MLS (multi-layer steel) gaskets (Six Star or Subaru OEM MLS 11044AA633). Machine both cylinder heads. Replace timing belt, water pump (21111AA370), thermostat, cam seals, and valve cover gaskets while the engine is apart. Use Subaru Cooling System Conditioner. Due to Baja rarity, keep the vehicle maintained - these are appreciating in value.

What you need to fix it

Only diagnosis- and fitment-reviewed repair parts are linked here.

  • Genuine Subaru 11044AA633 cylinder head gasket

    2003-2006 naturally aspirated Subaru Baja 2.5L only after VIN/engine confirmation; quantity two required. Do not expose this path for an EJ255 turbo repair merely because a broad retailer fitment table includes multiple Baja trims.

    SubaruPartsDeal

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Typical repair cost:$1,500 - $2,800
Sources for this issue (3)
  • 2003 Baja Replace EJ25 Head Gasket - Subaru Forester Ownersforum
  • Subaru Head Gasket Problems - Mechanic Basemedia
  • Subaru Head Gasket Problems Explained 1990-Present - Ultimate Subaruforum

Research This Issue

Based on 890 owner reports

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Community Reported
High Confidence890 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
All Subaru Baja known issues →
Link to this issueError Codes:P052EP0171

Owners report a strong oil, gasoline or hot-rubber smell from the engine bay, sometimes accompanied by oil seepage at the PCV hose joint. Subaru traced this to an undersized PCV hose clamp on the FA24F that allows blow-by vapors and oil mist to escape. TSB 11-204-23 prescribes a revised PCV hose assembly and improved spring clamp.

Common Symptoms

  • burning oil or fuel smell
  • hot rubber odor at idle
  • oily residue near PCV valve
  • occasional P052E / P0171 lean codes

How to Fix

Have the dealer perform TSB 11-204-23 (dated 04/25/2023): replace the PCV hose assembly (part 11815AC88D) which includes the new enlarged spring clamp. Covered under California Emissions Performance & Defect Warranty (5yr/50,000mi), Federal Emissions Performance Warranty (2yr/24,000mi), or otherwise the 3yr/36k Basic warranty for qualifying VINs.

What you need to fix it

Only diagnosis- and fitment-reviewed repair parts are linked here.

  • Genuine Subaru 11815AC88E PCV hose assembly

    2019-2025 Subaru Ascent 2.4L according to the live catalog, after VIN confirmation. Use new clamps and renew the TSB-specified disturbed gaskets as required; do not use this link as proof that every hot or fuel odor is a PCV-hose fault.

    SubaruPartsDeal

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Typical repair cost:$0 - $300
Sources for this issue (3)
  • TSB 11-204-23 PCV Hose Design Change (Ascent/Legacy/Outback Turbo)tsb
  • Burning Rubber Smell / Oil leak - Subaru Ascent Forumforum
  • Crankcase Ventilation Leak - Subaru Ascent Forumforum

Research This Issue

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Community Reported
High ConfidenceVerifiedReviewed Jun 2026
All Subaru Ascent known issues →

P0171 code reference

General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.

Frequently asked questions

What does P0171 mean on a Subaru?

P0171 stands for "System Too Lean (Bank 1)." This code means the engine's computer has detected that the air-fuel mixture on Bank 1 (the side of the engine with cylinder #1) is running too lean — meaning there is too much air relative to fuel. The computer watches the oxygen sensors and has had to add a large amount of extra fuel (long-term fuel trim) to try to compensate, but it has hit its correction limit. A lean condition can cause rough idle, hesitation, reduced power, and over time can run the engine hotter than normal. It usually points to either unmetered air leaking into the engine or not enough fuel being delivered. On Subaru it is documented across 8 models: Outback, Impreza, Legacy, Forester, WRX, Crosstrek, Baja, Ascent.

What are the most common causes of P0171?

The most common causes of P0171 are: Vacuum or intake air leak (cracked hose, gasket, or PCV system), Dirty or failing mass airflow (MAF) sensor, Weak fuel pump or restricted fuel filter, Clogged or dirty fuel injectors, Faulty or aged upstream oxygen sensor, Leaking intake manifold gasket, Low fuel pressure or failing fuel pressure regulator, Exhaust leak ahead of the oxygen sensor. The specific cause varies by vehicle.

How much does it cost to fix P0171 on a Subaru?

Published repair estimates on Subaru range from $1,200 to $10,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.

Related codes

  • P0172 · System Too Rich (Bank 1)
  • P0174 · System Too Lean (Bank 2)
  • P0175 · System Too Rich (Bank 2)
  • P017B · Cylinder Head Temperature Sensor - Implausible Signal
  • P0087 · Fuel Rail/System Pressure - Too Low
  • P0088 · Fuel Rail/System Pressure - Too High
  • P0130 · O2 Sensor Circuit Malfunction (Bank 1, Sensor 1)
  • P0131 · O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)

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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.

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