Au7o mascotAu7o
Known IssuesGet Started
  1. Au7o
  2. /
  3. Known Issues
  4. /
  5. DTC Codes
  6. /
  7. P0301
  8. /
  9. Subaru
Subaru · Engine · Moderate code

P0301 on Subaru: How to Diagnose & Fix

Cylinder 1 Misfire Detected

9 Subaru models · 18 documented issues · 11 critical · $60-$12,000 repair

Share:@au7o.io

P0301 by Subaru model

  • 1999-2025Outback3
  • 1993-2011Impreza3
  • 2000-2009Legacy1
  • 2003-2006Baja1
  • 2015-2021WRX STI1
  • 2013-2016BRZ1
  • 2006-2014Tribeca2
  • 1998-2025Forester5
  • 2015-2021WRX1
  • FAQ

P0301 on other makes

  • Acura
  • Alfa Romeo
  • Audi
  • Bmw
  • Buick
  • Cadillac
  • Chevrolet
  • Chrysler
  • Dodge
  • Ford
  • Genesis
  • Gmc
Diagnose my car
Back to top

P0301 by Subaru model

  • 1999-2025Outback3
  • 1993-2011Impreza3
  • 2000-2009Legacy1
  • 2003-2006Baja1
  • 2015-2021WRX STI1
  • 2013-2016BRZ1
  • 2006-2014Tribeca2
  • 1998-2025Forester5
  • 2015-2021WRX1
  • FAQ

P0301 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

GoogleRedditYouTubeNHTSA
Community Reported
High ConfidenceVerified4,521 owner reportsLast reported by owners Jan 2024Reviewed 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

GoogleRedditYouTubeNHTSA
Community Reported
Medium Confidence680 owner reportsLast reported by owners Feb 2023Reviewed Feb 2026
Link to this issueError Codes:P0300P0301P0302P0303P0304

The turbocharged FA24 (FA24F/FA24DIT) 2.4L boxer in Outback XT, Onyx Edition XT, and Wilderness trims uses port-less direct injection only, so fuel never washes the back of the intake valves. Carbon sludge accumulates on the intake ports/valves, typically becoming noticeable around 40,000-60,000 miles, causing rough idle, misfires, hesitation, and gradual power loss. Some owners also report elevated oil consumption on this engine, which accelerates deposit formation. Because no port injectors exist, fuel-additive cleaners do not reach the valves.

Common Symptoms

  • Rough or unstable idle
  • Cylinder misfire
  • Hesitation and reduced power
  • Check engine light (misfire codes)
  • Elevated oil consumption between changes

How to Fix

The effective remedy is mechanical cleaning — walnut-shell media blasting of the intake valves every ~50,000-60,000 miles (about $400-$1,200 depending on shop). Mitigate (not prevent) buildup with top-tier synthetic oil at shorter 4,000-5,000 mile intervals, top-tier fuel, and an occasional intake cleaner/Italian tune-up. Monitor oil level between changes given the engine's consumption tendency.

Typical repair cost:$400 - $1,200
Sources for this issue (3)
  • Subaru Outback Forums — FA24F engine (2.4L turbo) direct-injection design / carbon buildup discussionforum
  • Subaru Ascent Forum — FA24DIT direct injection carbon buildup still a thing?forum
  • Engine Explained — Subaru FA24 2.4L reliability and common problemsarticle

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
High ConfidenceVerifiedReviewed Jun 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

GoogleRedditYouTubeNHTSA
Community Reported
High Confidence4,200 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
Link to this issueError Codes:P0300P0301P0302P0303P0304

The SOHC EJ18 and EJ22 engines in the base 1990s Impreza use a camshaft-driven distributor. With age, the cap and rotor corrode and crack, and the distributor O-ring can weep oil into the cap. This causes crossfire and weak spark that shows up as rough idle, hesitation, and hard starting, classically worse in damp or rainy weather when moisture inside the cap promotes arcing. It is an inexpensive but frequently overlooked maintenance item on these high-mileage cars.

Common Symptoms

  • Rough idle and intermittent misfire
  • Hesitation or stumble under acceleration
  • Hard starting or stalling, worse in wet/humid weather
  • Check-engine light with misfire codes (OBD-II cars)

How to Fix

Replace the distributor cap, rotor, and spark plug wires (and plugs) with quality parts; on OBD-II cars this clears random/cylinder misfire codes. If oil is found inside the distributor, replace the distributor O-ring/seal. Keep ignition components dry and correctly seated.

Typical repair cost:$60 - $250
Sources for this issue (2)
  • EJ22 Distributor? - Ultimate Subaru Message Boardforum
  • EJ22 Random misfire when warmed - Ultimate Subaru Message Boardforum

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
Medium ConfidenceVerifiedReviewed Jul 2026
Link to this issueError Codes:P0128P0301P0300

The first-generation 2.5L DOHC boxer (EJ25D) used in the 1998-1999 Impreza 2.5 RS (and shared with the 1996-1999 Legacy/Outback/Forester of the era) is notorious for internal head gasket failure. In 1996 Subaru used a composite gasket, then from 1997 switched to a multi-layer-steel shim gasket with a graphite outer film; the film between the combustion chamber and the cooling jacket degrades (typically around 100,000 miles), allowing coolant into the combustion chamber and combustion gases into the cooling jacket. Because the flat-four has two heads and the failure is typically internal (coolant-to-combustion) rather than the external weep seen on the later 2.5 SOHC, the classic pattern is overheating on the highway that cools off in town, and it can warp a head if driven on. This is the defining reliability problem of the DOHC-era 1990s Impreza.

Common Symptoms

  • Overheating, especially on long freeway drives or climbing grades
  • Oily film or coolant loss in the overflow/expansion bottle
  • Exhaust, fuel, or sulfur smell in the coolant reservoir
  • Intermittent high coolant-temperature gauge readings
  • Coolant loss with no obvious external leak
  • White exhaust smoke / bubbling in the coolant

How to Fix

Replace both head gaskets with updated multi-layer-steel gaskets, resurface/pressure-test the heads, and replace the timing belt, water pump, and thermostat while the front of the engine is open. Many owners upgrade to the revised OEM gasket or a quality MLS gasket set. A cooling-system flush and new coolant conditioner is standard on reassembly.

What you need to fix it

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

  • Genuine Subaru 11044AA610 EJ25D Cylinder-Head Gasket

    updated OE head gasket for each bank after the EJ25D failure is confirmed Fitment/availability: 1998 Impreza 2.5 RS with 2.5-liter DOHC EJ25D; quantity two, not for the 1999 SOHC 2.5 RS Fitment/availability: ships in 1-3 business days wi…

    SubaruPartsDeal
  • Genuine Subaru 13028AA072 EJ25D Timing Belt

    timing belt when removed for repair, with tensioner and idlers selected from the VIN catalog Fitment/availability: 1998 Impreza 2.5 RS EJ25D only Fitment/availability: ships in 1-2 business days with Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 21111AA007 Water Pump

    water pump when failed, leaking, rough or due while the timing drive is open Fitment/availability: 1998 Impreza 2.5 RS EJ25D catalog branch; confirm VIN and gasket/sealing components Fitment/availability: ships in 1-3 business days with …

    SubaruPartsDeal
  • Genuine Subaru 21200AA072 Thermostat

    thermostat when testing, overheating history or age warrants replacement Fitment/availability: 1998 Impreza 2.5 RS EJ25D application; confirm VIN and use the correct thermostat gasket Fitment/availability: ships in 1-3 business days with…

    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:$1,200 - $2,600
Sources for this issue (3)
  • Subaru EJ25 Head Gasket Problems - Underhood Servicearticle
  • Head Gasket Problems Explained - RS25.com (Impreza GC8 & RS Forum)forum
  • 1997-1999 Subaru Legacy, Forester & Impreza 2.5L DOHC Cylinder Head & Head Gasket Failures - Go-Partsarticle

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
High ConfidenceVerifiedReviewed Jul 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

GoogleRedditYouTubeNHTSA
Community Reported
High Confidence3,800 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
All Subaru Legacy 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

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 (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

GoogleRedditYouTubeNHTSA
Community Reported
High Confidence890 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
All Subaru Baja known issues →
Community reported
780 owners
Link to this issueError Codes:P0300P0301P0302P0303P0304P0305P0306

The EJ257 engine in the STI is known for rod bearing failures, especially when modified or driven hard. The stock rod bearings have thin oil clearances and can spin under high load conditions. Oil starvation during hard cornering can accelerate bearing wear.

Common Symptoms

  • Knocking noise from bottom of engine
  • Low oil pressure warning
  • Metal shavings in oil
  • Sudden loss of power
  • Engine seizure in severe cases

How to Fix

Change oil every 3,000 miles with high-quality synthetic (Motul, Rotella T6). Install oil baffle or oil pan with baffle for track use. Consider upgraded rod bearings (ACL Race) if rebuilding. Monitor oil pressure and use oil analysis to catch wear early.

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:$5,000 - $12,000

Research This Issue

Based on 780 owner reports

GoogleRedditYouTubeNHTSA
Community Reported
High Confidence780 owner reportsLast reported by owners Feb 2024Reviewed Feb 2026
All Subaru WRX STI known issues →
Community reported
520 owners
Link to this issueError Codes:P0300P0301P0302P0303P0304P0305P0306

The FA20 engine in 2013-2016 BRZs was subject to a safety recall (WQG-66 / NHTSA 18V-845) for defective valve springs that can fracture due to insufficient hardness. A broken valve spring causes a cylinder misfire and can lead to engine stalling. In worst cases, the broken spring allows valve-to-piston contact, causing catastrophic engine damage. Subaru recalls affected VINs for free valve spring replacement. The recall also affects the Toyota 86/Scion FR-S which shares the same engine.

Common Symptoms

  • Engine misfire (single cylinder)
  • Check engine light with misfire code (P0301-P0304)
  • Rough idle or engine shaking
  • Loss of power
  • Engine stalling at idle or low speed
  • Ticking or unusual noise from engine top end

How to Fix

Check recall status by VIN at subaru.com/owners/recalls. Recall WQG-66 (NHTSA 18V-845) covers free replacement of all intake and exhaust valve springs (16 total) at Subaru dealer. If valve-to-piston contact occurred, engine replacement is covered under the recall. Do not delay - a broken valve spring can cause catastrophic engine damage.

Typical repair cost:$0 - $0
Sources for this issue (4)
  • frs recall regarding valve spring defect - FT86CLUBforum
  • Engines Keep Failing Subaru BRZ Valve Spring Recall - The Drivemedia
  • Subaru and Toyota to Recall Engine Issues - Consumer Reportsmedia
  • Toyota Subaru Face Class-Action Lawsuit Valve Spring Recall - Center for Auto Safetymedia

Research This Issue

Based on 520 owner reports

GoogleRedditYouTubeNHTSA
Community Reported
High Confidence520 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
All Subaru BRZ known issues →
Community reported
420 owners
Link to this issueError Codes:P0011P0012P0016P0300P0301P0302P0303P0304P0017P0018P0019

The 3.6L EZ36 flat-6 engine uses timing chains instead of belts, but the chains and guides are not maintenance-free as often assumed. The timing chain tensioner and plastic chain guides wear over time, typically after 120,000-180,000 miles. Worn chains stretch, causing rough idle, misfires, and timing-related codes. The EZ36 uses three timing chains (one for each bank plus one for the center) making replacement a complex and labor-intensive job. If a chain jumps timing due to severe stretch or guide failure, valve-to-piston contact can cause catastrophic engine damage.

Common Symptoms

  • Rattling or chattering noise from front of engine on cold start
  • Rough idle that improves as engine warms
  • Check engine light with timing correlation codes (P0016, P0017, P0018, P0019)
  • Reduced engine performance
  • Engine misfires at idle
  • Chain noise that increases over time

How to Fix

Replace all three timing chains, chain tensioners (3 units), chain guides (6 pieces), and chain tensioner shoes. This is a major job requiring 12-16 hours of labor. Use genuine Subaru timing chain kit or quality aftermarket (OSK brand). Replace water pump, thermostat, and front crank seal while the front of the engine is disassembled. Total repair with all components: $2,500-4,000 at an independent shop.

What you need to fix it

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

  • Genuine Subaru 13143AA071 Timing Chain

    one of three required chains after mechanical timing diagnosis Fitment/availability: 2008-2014 Tribeca 3.6-liter EZ36; current replacement for 13143AA070, confirm VIN/production date Fitment/availability: ships in 1-3 business days with …

    SubaruPartsDeal
  • Genuine Subaru 13143AA081 Timing Chain

    second timing chain after diagnosis Fitment/availability: 2008-2014 Tribeca 3.6-liter EZ36; current replacement for 13143AA080, confirm VIN/production date Fitment/availability: ships in 1-3 business days with Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 13143AA061 Timing Chain

    third timing chain after diagnosis Fitment/availability: 2008-2014 Tribeca 3.6-liter EZ36; current replacement for 13143AA060, confirm VIN/production date Fitment/availability: ships in 1-3 business days with Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 13142AA050 Timing Chain Tensioner

    one of three position-specific tensioners Fitment/availability: 2008-2014 Tribeca 3.6-liter EZ36, position 13142; confirm VIN Fitment/availability: ships in 1-3 business days with Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 13142AA040 Timing Chain Tensioner

    second position-specific tensioner Fitment/availability: 2008-2014 Tribeca 3.6-liter EZ36, position 13142B; confirm VIN Fitment/availability: ships in 1-3 business days with Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 13142AA080 Timing Chain Tensioner

    third position-specific tensioner Fitment/availability: 2008-2014 Tribeca 3.6-liter EZ36, position 13142A; 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.

Typical repair cost:$2,500 - $4,500
Sources for this issue (4)
  • 2008 3.6L Timing - Subaru B9 Tribeca SUV Forumforum
  • 3.0 H6 Timing Chain and Guide Discussion - Subaru Outback Forumsforum
  • Subaru Tribeca Bad Timing Belt or Chain Symptoms - Drivetrain Resourcemedia
  • 2006 H-6 3.0 Timing Chain renewal - Subaru B9 Tribecaforum

Research This Issue

Based on 420 owner reports

GoogleRedditYouTubeNHTSA
Community Reported
High Confidence420 owner reportsLast reported by owners Feb 2026Reviewed Feb 2026
Link to this issueError Codes:P0300P0301P0302P0303P0304P0305P0306

The 2006-2007 Subaru Tribeca with the 3.0L EZ30 flat-6 engine can develop head gasket leaks, typically at higher mileages (130,000-200,000 miles). While the EZ30 is generally more resistant to head gasket issues than the smaller EJ25 boxer engines, the problem does occur. The flat-6 boxer design means the head gaskets are oriented horizontally, which allows coolant to seep past the gasket under gravity when the engine is off. Symptoms include external oil leaks between the head and block, coolant consumption, and in severe cases, coolant entering the combustion chamber causing white exhaust smoke and overheating. The repair is complex due to the flat-6 layout and cramped engine bay of the Tribeca.

Common Symptoms

  • Oil seeping between cylinder head and engine block
  • Coolant level dropping without visible external leaks
  • White exhaust smoke (coolant burning in combustion chamber)
  • Heater blowing cold air intermittently (air trapped in cooling system)
  • Engine overheating
  • Sweet coolant smell from engine bay
  • Temperature gauge fluctuations

How to Fix

Typical repair cost:$2,500 - $4,000
Sources for this issue (1)
  • YouTube video by EricTheCarGuy on diagnosing and repairing Subaru EZ30 head gasket leaksvideo

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
Medium Confidence
All Subaru Tribeca known issues →
Link to this issueError Codes:P0301P0302P0303P0304P0351P0352P0353P0354P0300

Coil-on-plug ignition coils on the Forester are a common failure point. As the coil's internal epoxy/resin cracks with heat and age, the coil produces erratic or insufficient spark, causing single-cylinder misfires, rough idle, hesitation on acceleration, reduced fuel economy and a flashing/steady check-engine light. A frequently reported pattern is hard starting or stumbling when cold (below roughly 10°F) that improves once the engine warms. Note that a leaking spark plug tube seal (oil in the plug well) can prematurely kill a coil, so the two issues often appear together.

Common Symptoms

  • Rough idle and vibration at idle
  • Engine hesitation or stumble on acceleration
  • Flashing or steady check engine light
  • Hard starting or misfire when cold
  • Reduced fuel economy

How to Fix

Pull codes — P0301-P0304 indicate the misfiring cylinder; P0351-P0354 indicate coil circuit faults. Confirm by swapping the suspect coil to an adjacent cylinder; if the misfire follows the coil, replace it (coils cannot be repaired). Inspect the plug well for oil and replace the spark plug tube seal if oil is present so the new coil isn't ruined. Replace the spark plugs at the same time. Forester ignition coil part numbers vary by year/engine (for example 22433AA691 on 2013-2018 2.5L and 22433AA590 on non-turbo 2009-2010); confirm the exact PN by VIN.

What you need to fix it

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

  • Genuine Subaru 22433AA590 Ignition Coil

    single-cylinder replacement after the coil is proven failed Fitment/availability: 2009-2010 Forester 2.5L naturally aspirated X/X Limited/XS branch only; not XT, confirm VIN Fitment/availability: Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 22433AA630 Ignition Coil

    single-cylinder replacement after the coil is proven failed Fitment/availability: 2011-2013 Forester 2.5L naturally aspirated X/X Limited/X Premium branch; not XT, confirm VIN Fitment/availability: ships in 1-2 business days with Add to …

    SubaruPartsDeal
  • Genuine Subaru 22433AA682 Ignition Coil

    single-cylinder replacement after the coil is proven failed Fitment/availability: 2014-2016 Forester 2.5i naturally aspirated branch; current replacement for 22433AA681/AA680, confirm VIN Fitment/availability: ships in 1-2 business days …

    SubaruPartsDeal
  • Genuine Subaru 22433AA700 Ignition Coil

    single-cylinder replacement after the coil is proven failed Fitment/availability: 2017-2018 Forester 2.5i naturally aspirated branch in this issue; retailer also catalogs XT, confirm VIN Fitment/availability: Add to Cart live when reviewed

    SubaruPartsDeal
  • Genuine Subaru 22433AA770 Ignition Coil

    single-cylinder replacement after the coil is proven failed Fitment/availability: 2019-2021 Forester Base/Premium/Sport/Limited/Touring branch; confirm VIN and production split Fitment/availability: ships in 1-3 business days with Add to…

    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:$60 - $350
Sources for this issue (3)
  • Subaru Forester bad ignition coils symptoms, causes, and diagnosis - WheelsJointforum
  • 2012 - Rough idle, occasional P0301, misfires on hot start - Subaru Forester Owners Forumforum
  • 2014-2016 Subaru Forester Ignition Coil 22433AA691 - OEM Parts Onlinemanufacturer

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
Medium ConfidenceVerifiedReviewed Jun 2026
Link to this issueError Codes:P0300P0301P0302P0303P0304

For 2019 the SK Forester switched the FB25 from port injection to direct injection. With no fuel washing over the back of the intake valves, oil vapor from the PCV system bakes onto the valves and ports as hard carbon. Deposits restrict airflow and disturb valve sealing, and once buildup gets severe owners report a rough idle, stumbling, and misfire codes — often only on cold start at first. This is not the FB25 excessive-oil-consumption story from the port-injected 2011-2018 engines; it is a deposit problem specific to the direct-injected FB25 in the 2019+ car, and it appears alongside the higher oil-dilution readings typical of DI boxers driven on short trips. It is a known trait of all GDI engines, not a Subaru-unique defect, but it does have a real service interval attached to it.

Common Symptoms

  • Rough or unstable idle
  • Cold-start stumble
  • Misfire codes
  • Hesitation under light throttle
  • Gradual loss of power and fuel economy

How to Fix

There is no recall or warranty program. Preventive: run an induction/intake cleaning service (BG or equivalent) periodically — shops commonly recommend around every 30,000 miles at roughly $130-$160 — and avoid a diet of short cold trips, which maximizes both deposits and oil dilution. Corrective: when misfires and rough idle appear, the fix is mechanical cleaning of the intake valves — walnut blasting with the intake manifold removed — typically recommended around 100,000-120,000 miles. Chemical top-engine cleaners help only mild deposits. Replace fouled plugs and inspect the PCV valve at the same time.

Typical repair cost:$150 - $900
Sources for this issue (3)
  • 2019+ Carbon Buildup? (merged thread) — Subaru Forester Owners Forumforum
  • 2019 2.5L Engine Direct Injection? — Subaru Forester Owners Forumforum
  • The 3 Most Common Subaru FB25 Engine Problems — 8020 Automotivearticle

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
High ConfidenceVerifiedReviewed Aug 2026
Link to this issueError Codes:P0301P0302P0303P0304

The first-generation 2.5L DOHC boxer (EJ25D/EJ25DZ) fitted to the 1998-1999 SF Forester used a composite head gasket that fails INTERNALLY — between the coolant and oil galleries, or coolant into the combustion chamber — rather than the slow external seep that the later SOHC EJ251/EJ253 engines are known for. This is a genuinely different failure from the well-known SOHC external head-gasket leak: the DOHC version gives little warning, and once it lets go the engine overheats and is undriveable almost immediately. Subaru dropped the DOHC 2.5 in the Forester after 1999 partly because of it. Owners see milky oil, coolant loss with no visible drip, exhaust steam and pressurized overflow tank. Because the EJ25D is an interference design, a resulting overheat can warp heads and cook bearings.

Common Symptoms

  • Milky/creamy oil on dipstick or filler cap
  • Coolant loss with no visible external leak
  • Overheating within minutes of the failure
  • White steam from exhaust
  • Overflow tank bubbling or pressurizing
  • Sudden loss of coolant level after a hot run

How to Fix

Confirm with a combustion-gas (block) test of the coolant and a cooling-system pressure test before teardown — internal failures show gases in coolant with no external stain. Repair is a full head-gasket job with both heads pressure-tested and resurfaced by a machine shop, and replacement with the later multi-layer-steel (MLS) gasket set rather than the original composite gasket. Because access requires the timing belt to come off, replace the belt, water pump, tensioner and idler pulleys at the same time. Subaru's coolant-conditioner service campaign of the era addressed only the external SOHC leak and does not remedy this failure. No free recall remedy exists. On a high-mileage car, a good used or remanufactured long block is often cheaper than a proper head job.

Typical repair cost:$1,600 - $3,500
Sources for this issue (3)
  • How to replace EJ25 head gaskets without removing engine — Subaru Forester Owners Forumforum
  • Subaru EJ25 Head Gasket Problems — Underhood Servicearticle
  • DIY: 99-10 EJ25 SOHC Head Gaskets — Subaru Forester Owners Forumforum

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
Low ConfidenceVerifiedReviewed Aug 2026
Link to this issueError Codes:P0301P0302P0303P0304

The turbocharged EJ255 has thin, cast-piston ringlands that crack under detonation. The large bore, high cylinder temperatures and a flat oil pan that lets oil slosh away from the pickup under cornering make the engine vulnerable: a single knock event (low-octane fuel, poor tune, hard driving, or oil starvation) can fracture the second ringland. Once cracked, combustion gases blow into the crankcase and oil consumption spikes to roughly a quart every 300-500 miles, with misfires and eventual catastrophic engine failure.

Common Symptoms

  • Heavy oil consumption (quart per 300-500 miles)
  • Cylinder misfire and rough running
  • Blue exhaust smoke
  • Loss of power / failed leakdown on one cylinder
  • Engine knock under load

How to Fix

Run only the required premium fuel, change oil on short synthetic intervals, address any knock/detonation immediately, and avoid extended high-boost driving on a stock bottom end. A cracked ringland is confirmed by a leakdown/compression test on the affected cylinder; the repair is a rebuild or replacement of the short block with upgraded forged pistons. Adding an oil-pickup baffle/extended sump helps prevent recurrence.

Typical repair cost:$4,000 - $8,000
Sources for this issue (3)
  • 05 XT Ring land failure — Subaru Outback/Forester forumforum
  • How to Avoid Ringland Failure in your Subaru — Come and Drive Itarticle
  • Suggestions needed, piston rings are going bad — Subaru Forester Owners Forumforum

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
Medium ConfidenceVerifiedReviewed Jun 2026
Link to this issueError Codes:P0300P0301P0302P0303P0304

The boxer engine's two valve covers face outward and sit low on each side, exposing the cork/rubber valve cover gaskets and the spark plug tube seals to heat cycling and the path of any leaking oil. As these seals harden and shrink, oil seeps out and visibly drips onto the exhaust (burning-oil smell from under the hood) and — more importantly — pools down inside the spark plug tubes. Oil in the plug tubes saturates the plugs, boots and ignition coils, leading to engine misfires, rough idle and a check-engine light. Owners report this on both early FB25s and surprisingly low-mileage newer cars (cases as early as ~17k-50k miles documented on the owners' forum). The valve cover's external location makes the leak a frequent dealer/independent repair.

Common Symptoms

  • Burning oil smell from engine bay
  • Oil dripping/residue along the lower side of the engine
  • Rough idle and engine misfire
  • Check engine light with cylinder misfire codes
  • Oil pooled in spark plug wells when coils are removed

How to Fix

Remove the affected valve cover and replace BOTH the valve cover gasket AND the spark plug tube seals at the same time (replacing only the cover gasket and leaving old tube seals lets oil keep reaching the plugs). Inspect and replace any oil-soaked spark plugs and ignition coils. The FB25 valve cover gasket is OEM 13294AA050 (supersedes/cross to 13294AA053); the gasket set that includes the spark plug tube/washer seal is 13293AA051. Clean oil residue off the block and re-torque the cover to spec.

What you need to fix it

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

  • Genuine Subaru 13272AA170 Left Valve-Cover Gasket

    left cover perimeter gasket when that side is confirmed leaking Fitment/availability: 2011-2018 Forester FB25 left/driver-side branch; confirm VIN and engine Fitment/availability: Add to Cart live when reviewed

    Subaru Parts For You
  • Genuine Subaru 13270AA240 Right Valve-Cover Gasket

    right cover perimeter gasket when that side is confirmed leaking Fitment/availability: 2011-2018 Forester 2.5-liter naturally aspirated FB25 right/passenger-side branch; confirm VIN Fitment/availability: ships in 1-3 business days with A…

    SubaruPartsDeal
  • Genuine Subaru 13272AA250 Left Valve-Cover Gasket

    left cover perimeter gasket when that side is confirmed leaking Fitment/availability: Retailer explicitly lists 2019-2025 Forester; use here for the 2019-2024 FB25D left-side branch and confirm VIN Fitment/availability: two left with Add…

    Subimods
  • Genuine Subaru 13270AA300 Right Valve-Cover Gasket

    right cover perimeter gasket when that side is confirmed leaking Fitment/availability: Retailer explicitly lists 2019-2025 Forester; use here for the 2019-2024 FB25D right-side branch and confirm VIN Fitment/availability: two left with A…

    Subimods

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:$250 - $700
Sources for this issue (3)
  • 2024 - 17k miles - oil leak, valve cover, all spark plugs, tubing? - Subaru Forester Owners Forumforum
  • Worn Out Gaskets Allowed Oil to Seep Into Spark Plugs: Subaru Forester - RepairPalarticle
  • 13293AA051 - Engine Valve Cover Gasket / Washer Seal - Genuine Subaru Partmanufacturer

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
Medium ConfidenceVerifiedReviewed Jun 2026
All Subaru Forester known issues →
Link to this issueError Codes:P0300P0301P0302P0303P0304

The 2015-2021 WRX's FA20DIT is direct-injected, so no fuel washes over the backs of the intake valves. Oil vapor from the PCV system and blow-by bakes onto the valves and ports, and owners tearing into engines at 40k-80k miles find heavy coking. Symptoms build gradually: rough cold idle, intermittent misfire codes, hesitation, and measurable horsepower loss on the dyno. Dealers typically deny it as a warranty defect since it is treated as a maintenance condition. This is specific to the FA20DIT; the port-injected EJ255 WRX does not coke intake valves this way.

Common Symptoms

  • Rough idle when cold
  • Intermittent misfire codes
  • Hesitation on tip-in
  • Gradual loss of power
  • Poor fuel economy

How to Fix

Physically clean the valves — walnut-shell blasting with the intake manifold and TGVs removed is the accepted fix; fuel additives cannot reach the valve backs on a DI engine. Many owners install an oil catch can or air-oil separator on the PCV line to slow recurrence. Replace spark plugs and inspect for misfire damage while apart. No recall or extended-warranty remedy.

Typical repair cost:$400 - $1,200
Sources for this issue (4)
  • Carbon Build Up On Valves - NASIOCforum
  • Walnut Blasting Intake Valves for 2015+ WRX FA20 DIT - ClubWRXforum
  • 2015+ WRX have carbon build problems? - IWSTIforum
  • FA20DIT Common Problems and Reliability: 2015-2021 Subaru WRXarticle

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
High ConfidenceVerifiedReviewed Sep 2026
All Subaru WRX known issues →

P0301 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 P0301 mean on a Subaru?

P0301 stands for "Cylinder 1 Misfire Detected." P0301 means the engine computer detected a misfire specifically in cylinder 1 — the spark didn't ignite the fuel properly, or the fuel/air mix didn't burn as it should. The computer detects this by sensing tiny variations in crankshaft speed each time a cylinder fires. A misfire wastes fuel, raises emissions, and can damage the catalytic converter if it's severe or persistent (a flashing check engine light usually warns of active, converter-damaging misfires). Because the code points to one specific cylinder, the cause is usually an ignition, fuel, or compression problem isolated to that cylinder. On Subaru it is documented across 9 models: Outback, Impreza, Legacy, Baja, WRX STI, BRZ, Tribeca, Forester, WRX.

What are the most common causes of P0301?

The most common causes of P0301 are: Worn or fouled spark plug in cylinder 1, Failed ignition coil or coil pack for cylinder 1, Faulty or clogged fuel injector for cylinder 1, Vacuum or intake air leak affecting that cylinder, Bad spark plug wire (on applicable engines), Low compression (worn rings, leaking or burnt valve, head gasket), Carbon buildup on intake valves, Wiring or connector fault to the coil or injector. The specific cause varies by vehicle.

How much does it cost to fix P0301 on a Subaru?

Published repair estimates on Subaru range from $60 to $12,000 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

  • P0300 · Random/Multiple Cylinder Misfire Detected
  • P0302 · Cylinder 2 Misfire Detected
  • P0303 · Cylinder 3 Misfire Detected
  • P0304 · Cylinder 4 Misfire Detected
  • 00522 · Engine Coolant Temperature Sensor (G62): Open Circuit / Short to Positive (B+)
  • 16500 · Engine Coolant Temp. Sensor (G62): Implausible Signal
  • 16502 · Engine Coolant Temperature Sensor (G62): Signal too High
  • 16566 · Mass Air Flow Sensor Signal Too Low (VAG)

Looking for P0301 on a different make?

View P0301 across all makes →
🔧
A mechanic who knows YOUR exact car
Answers tuned to your year, make, model & trim — not generic advice. Save your garage so it always has the right context.
Get notified about P0301 fixes on Subaru
We add new causes, fixes and affected Subaru models for P0301 regularly — drop your email and we'll keep you posted. You can also diagnose your own car free.

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

Known IssuesMotorcycle IssuesDTC LookupDrivePricingAboutTermsPrivacyCookiesConsentData rightsCopyrightFeedback
Share:@au7o.io

Vehicle data and repair guidance on this site are compiled with AI assistance and may contain errors. Always verify with your service manual or a qualified mechanic.

Data protection representation

DataRep representative in the United KingdomDataRep representative in the European Union
Au7o · 2026
Built for DIY mechanics. Privacy-first.
Explore free Hub demo