P0306 on Subaru
Cylinder 6 Misfire Detected
P0306 on Subaru vehicles indicates cylinder 6 misfire detected. Au7o has documented this code across 3 Subaru models — most commonly on BRZ, Tribeca, WRX STI. This code means the engine computer detected a misfire on cylinder 6 — that cylinder isn't burning its fuel-air mixture properly. The computer senses misfires by watching for tiny variations in crankshaft speed each time a cylinder should fire, and when cylinder 6 repeatedly fails to contribute, this code sets. You may feel a shake or stumble, especially at idle or under load, along with reduced power and possibly a flashing check-engine light, which signals a misfire severe enough to damage the catalytic converter. A misfire comes down to a problem with spark, fuel, or compression in that cylinder. Typical repair costs on Subaru range from $2,500 to $12,000, depending on the specific model and root cause.
Common Causes of P0306
- •Worn or fouled spark plug on cylinder 6
- •Failed ignition coil for cylinder 6
- •Clogged, leaking, or failed fuel injector
- •Vacuum or intake air leak affecting that cylinder
- •Low compression (worn rings, burnt valve, head gasket)
- •Damaged plug wire or coil connector
- •Carbon buildup or worn valvetrain components
P0306 on Subaru by Model
Subaru BRZ(1 issue)
- FA20 Valve Spring Recall - Engine Stalling Risk2013-2016
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.
Subaru Tribeca(1 issue)
- EZ30 3.0L H6 Head Gasket Leak2006-2007
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.
Subaru WRX STI(1 issue)
- Spun Rod Bearing Failure (EJ257)2015-2021
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.
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View P0306 across all makes →Frequently Asked Questions
What does P0306 mean on Subaru?▼
P0306 stands for "Cylinder 6 Misfire Detected." This code means the engine computer detected a misfire on cylinder 6 — that cylinder isn't burning its fuel-air mixture properly. The computer senses misfires by watching for tiny variations in crankshaft speed each time a cylinder should fire, and when cylinder 6 repeatedly fails to contribute, this code sets. You may feel a shake or stumble, especially at idle or under load, along with reduced power and possibly a flashing check-engine light, which signals a misfire severe enough to damage the catalytic converter. A misfire comes down to a problem with spark, fuel, or compression in that cylinder. On Subaru specifically, this code is documented across 3 models.
What causes P0306 on Subaru vehicles?▼
Common causes on Subaru: Worn or fouled spark plug on cylinder 6, Failed ignition coil for cylinder 6, Clogged, leaking, or failed fuel injector, Vacuum or intake air leak affecting that cylinder, Low compression (worn rings, burnt valve, head gasket). Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0306 on a Subaru?▼
Repair costs on Subaru range from $2,500 to $12,000, depending on the specific model and root cause.
Which Subaru models have P0306 documented?▼
Au7o has documented P0306 on 3 Subaru models: BRZ, Tribeca, WRX STI.