P0303: How to Diagnose & Fix — Cylinder 3 Misfire Detected
182 vehicles · 37 makes · $20-$15,000 repair
How to diagnose and fix P0303: most-reported vehicles
Ranked by owner reports. Each card gives the symptoms, how to confirm the cause, the fix, parts and sources for that vehicle.
Volkswagen Golf · 2008–2021
All EA888 direct-injection 2.0T engines suffer from carbon buildup on the intake valves because fuel is injected directly into the combustion chamber rather than sprayed over the valves. Without fuel washing, oil vapors from the PCV system bake onto the intake valves, reducing airflow and causing drivability issues. Buildup becomes noticeable around 40,000-60,000 miles. Gen3 EA888 engines sold outside North America added port injection, but North American Gen3 engines remained direct-injection only, so the problem persists on US cars.
Common Symptoms
- Rough idle
- Hesitation on acceleration
- Misfires (codes P0300-P0304)
- Reduced fuel economy
- Loss of power especially at low RPM
- Check engine light
How to Fix
Walnut shell blasting of intake valves is the most effective treatment ($400-700 at a shop). Some owners use chemical cleaning kits (Revive Turbo Cleaner, CRC GDI IVD Intake Valve Cleaner). Prevention: install a catch can to reduce oil vapor reaching the valves, and perform walnut blasting every 40,000-60,000 miles. Dual-injection Gen3 EA888 engines (non-North American markets) have reduced but not eliminated the problem.
Sources for this issue (2)
Land Rover Freelander · 2002–2005
The Rover KV6 2.5L V6 engine used in the Freelander is notorious for head gasket failure. The V6 design uses two head gaskets (front and rear banks) and the rear bank is particularly prone to failure. The aluminum heads warp from overheating, and the original gaskets deteriorate. Head gasket failure causes coolant and oil mixing, overheating, and eventual engine destruction if not addressed. This is the single most well-known Freelander issue.
Common Symptoms
- Overheating especially in traffic
- White smoke from exhaust
- Milky residue under oil filler cap
- Coolant loss with no visible leak
- Oil in coolant or coolant in oil
- Rough running and misfires
How to Fix
Replace both head gaskets with the updated multi-layer steel (MLS) design. Have both cylinder heads pressure-tested and skimmed for flatness. Replace the head bolts (they are torque-to-yield and cannot be reused). Also replace the thermostat and water pump while the engine is apart. Consider installing an aluminum radiator to prevent future overheating.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- ZUA001480 KV6 cylinder-head-gasket overhaul kitOEMZUA001480
Verify build details and all ancillary seals before teardown.
- LDN10027P1SET KV6 cylinder-head bolt setOEMLDN10027P1SET
Replace the full engine set of 16 KV6 stretch head bolts Fitment/availability: Freelander 1 2.5 KV6 petrol; one engine set.
- PEM000030PK complete KV6 thermostat and pipe kitOEMPEM000030PK
Renew a leaking or degraded thermostat assembly and the failure-prone connecting pipes during the cooling repair Fitment/availability: Freelander 1 2.5 KV6 petrol; includes thermostat, angled and straight coolant pipes, manifold gaskets …
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
- WarningIf you are buying a Freelander with the V6, check for head gasket failure BEFORE purchase. Budget $2,000-3,000 for the repair if it has not been done.
Sources for this issue (6)
- MG-Rover: Land Rover Freelander V6 head gasket failureforum
- Freelander Specialist: Freelander 2.5 Petrol K V6 Head Gasket Replacementmanufacturer
- LandyZone: KV6 engine reliability after re-designforum
- LandyZone: Freelander 1 KV6 Head Gasket failureforum
- Land Rovers Only: 2003 Freelander KV6 2.5 blown head gasket repairforum
- LandyZone: 2001 Freelander 2.5KV6 troubles?forum
Subaru Outback · 1999–2010
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…
- 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…
- 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 …
- 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
- 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 …
- 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…
- 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…
- 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…
- 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…
- 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
- 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…
- 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
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
Sources for this issue (4)
MINI Cooper S · 2007–2013
Mazda MX-5 Miata · 1999–2005
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P0303 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 P0303 mean?
P0303 stands for "Cylinder 3 Misfire Detected." This code means your engine's computer detected a misfire specifically in cylinder number 3 — that cylinder isn't burning its fuel-air mixture properly or completely. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder is supposed to fire. A misfire wastes fuel, can cause a noticeable shake, rough idle or loss of power, and can flood raw fuel into the exhaust where it may overheat and damage the catalytic converter. Because the fault is isolated to one cylinder, the cause is usually something specific to that cylinder's ignition, fuel delivery, or compression.
What are the most common causes of P0303?
The most common causes of P0303 are: Worn or fouled spark plug in cylinder 3, Failed or weak ignition coil on cylinder 3, Bad spark plug wire or boot (where applicable), Clogged or leaking fuel injector for cylinder 3, Vacuum or intake air leak affecting that cylinder, Low compression (worn rings, burnt/leaking valve, head gasket), Wiring or connector fault at the coil or injector. The specific cause varies by vehicle.
How much does it cost to fix P0303?
Repair costs for P0303 range from $20 to $15,000, depending on the vehicle and root cause.
Which vehicles are affected by P0303?
Au7o has documented P0303 across 182 vehicle models from 37 manufacturers: Acura, Alfa Romeo, Audi, BMW, Buick, Cadillac, Chevrolet, Chrysler, Dodge, Ford, GMC, Genesis, Honda, Hyundai, Infiniti, Jaguar, Jeep, Kia, Land Rover, Lexus, Lincoln, MINI, Mazda, Mercedes-Benz, Nissan, Peugeot, Pontiac, Porsche, RAM, Saab, Saturn, Skoda, Subaru, Suzuki, Toyota, Volkswagen, Volvo.
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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.