A knocking sound from your 2021 Outback's boxer engine combined with a P0302 misfire code demands attention. The horizontal engine layout means cylinder 2 is on the passenger side of the engine, and determining whether you're hearing actual knock or misfire noise is the first diagnostic step.
Knock vs. Misfire Sound
Engine knock:
- Metallic pinging or rattling
- Worse under acceleration/load
- Often heat-related
- Can indicate serious internal damage
Misfire sound:
- Irregular exhaust note (putt-putt)
- Rough running/vibration
- Consistent at idle and acceleration
- Usually ignition or fuel related
What P0302 Indicates
The P0302 code points specifically to cylinder 2 misfiring. On the boxer engine, this is the front cylinder on the passenger (right) side. Focus your investigation there.
Common Causes of Cylinder 2 Issues
- Failed ignition coil - Coil pack not producing spark
- Worn spark plug - Plug in cylinder 2 worn or fouled
- Fuel injector problem - Clogged or stuck injector
- Compression loss - Valve or head gasket issue
- Wiring damage - Rodent damage to coil wiring
Rodent Damage Note
Subarus are known to attract rodents who chew wiring. In the Outback, ignition coil wiring runs near the engine where rodents nest. Inspect wiring carefully.
Diagnostic Steps
- Swap cylinder 2 coil with cylinder 4
- Clear code and run engine
- If misfire moves to cylinder 4, replace coil
- If P0302 remains, check plug and injector
- Inspect wiring for rodent damage
- Compression test if other causes ruled out
Repair Costs
- Ignition coil: $75-$175
- Spark plug: $25-$50
- Fuel injector: $150-$350
- Wiring repair: $100-$300
- Compression-related: $500-$2,000+