P0305 on Subaru: How to Diagnose & Fix
Cylinder 5 Misfire Detected
2 Subaru models · 2 documented issues · 2 critical · $2,500-$12,000 repair
P0305 on Subaru by model: symptoms, diagnosis and fix
The EJ257 2.5L turbo engine in the WRX STI is known for connecting-rod (and sometimes main) bearing failures, especially on cars that are tracked, modified or driven hard. Specialists list several possible causes rather than one: low oil level from leaks or oil consumption, low oil pressure from a damaged pickup, pump or seal, oil starvation in hard cornering, braking or sustained high load, contaminated oil or debris left from an earlier failure, heat from repeated track use, and detonation from poor fuel or a tune that doesn't match the hardware. A cracked factory oil pickup, which can let oil pressure fall, is another listed cause. Once a bearing is damaged it can spin, which can damage the crankshaft as well. Subaru bulletin 02-181-19 (March 2019) cites "an identified condition that can lead to isolated crankshaft bearing (main and / or connecting rod bearing) failures" on turbocharged 2.5L EJ short blocks and extends the powertrain warranty for them. A class-action settlement over the same bearing failures covered 2012-2017 WRX/WRX STI.
Common Symptoms
- Deep, rhythmic knock from the bottom of the engine that changes with RPM, often louder when warm or under load
- Low or fluctuating oil pressure / oil pressure warning
- Metal in the oil or oil filter
- Sudden oil consumption or smoke
- Rough running or misfires along with a new engine noise
- Engine seizure in severe cases
How to Fix
If a deep, rhythmic knock from the bottom of the engine appears, especially one that changes with RPM, stop driving and have the car towed. If the oil-pressure light comes on, shut the engine off as soon as it is safe. Don't add thicker oil to quiet the knock, and don't clear warning lights. Check these first: (1) the oil level on level ground, noting any leaks or recent top-ups (adding oil does not undo bearing damage); (2) stored and pending codes, scanned before anyone disconnects the battery; (3) a mechanical oil-pressure test at the specified temperature and conditions; (4) the oil, and the filter cut open, for metal. A knock alone is not a diagnosis. Ringland failure, piston slap, valvetrain noise or turbo noise can sound similar, so confirm the cause before buying parts. Repair: replacing only the bearings is possible in some cases, but only after the engine is inspected. If a bearing has spun or the crank is damaged, the fix may be crank machining or a replacement crank, a short block, or a complete engine. Ask the shop to measure clearances and to fix the root cause (for example a cracked oil pickup, low oil pressure, a bad tune or contaminated oil) before reassembly. Otherwise the new bearings can fail the same way. Warranty: Subaru bulletin 02-181-19 extended the powertrain warranty on the turbo 2.5L EJ short block from 5 years/60,000 miles to 8 years/100,000 miles (whichever comes first) for main and connecting-rod bearing failures. The settlement it relates to covered 2012-2017 WRX/WRX STI built between Oct. 11, 2011 and Nov. 16, 2016. That includes 2015-2016 and early 2017 STIs, but not 2018-2021. Cars with modified ECU software or piggyback devices were excluded. Most covered cars are now past 8 years, so check eligibility by VIN with a Subaru dealer. Under the settlement, repairs at an independent shop were reimbursed only if the car went to a Subaru dealer first, and short-block repairs were capped at $3,500 to $6,500 depending on what else was replaced. Prevention: check the oil level often, especially before hard driving, and look into any leaks or oil consumption. Use the specified oil and change interval, and use oil analysis to catch bearing wear early. Keep the tune matched to the fuel and hardware. Watch oil pressure and temperature on the track, and install an oil baffle or a baffled oil pan if the car is tracked.
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
Sources for this issue (4)
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
Confirm the diagnosis before committing to the repair: a cooling-system pressure test, a combustion-gas (block) test for coolant leaks, and a compression or leak-down test. Also rule out other external oil leak sources, such as the valve covers. The fix is replacing the head gaskets. Owners on CarComplaints report about $3,500 at around 128,000 miles, and some judged the repair not worth it on high-mileage vehicles. Fix any cause of overheating at the same time.
Sources for this issue (1)
P0305 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 P0305 mean on a Subaru?
P0305 stands for "Cylinder 5 Misfire Detected." This code means the engine control module detected a misfire on cylinder number 5, meaning that cylinder is not burning its air-fuel mixture properly on some combustion cycles. The computer senses misfires by watching for tiny fluctuations in crankshaft speed each time a cylinder fails to fire correctly. A misfire wastes fuel, can make the engine run rough or shake, and dumps unburned fuel into the exhaust, which can overheat and damage the catalytic converter. It generally points to a problem with spark, fuel delivery, or compression specifically affecting cylinder 5. On Subaru it is documented across 2 models: WRX STI, Tribeca.
What are the most common causes of P0305?
The most common causes of P0305 are: Worn or fouled spark plug on cylinder 5, Failed ignition coil or coil pack for cylinder 5, Faulty or clogged fuel injector on cylinder 5, Vacuum or intake air leak affecting that cylinder, Bad spark plug wire or boot (on applicable engines), Low compression from worn rings, valves, or head gasket, Carbon buildup or sticking valve on cylinder 5, Lean or rich fuel condition affecting the cylinder. The specific cause varies by vehicle.
How much does it cost to fix P0305 on a Subaru?
Published repair estimates on Subaru range from $2,500 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.
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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.