P0300 on Subaru: Random or Multiple Cylinder Misfire Detected
Severity: 3 of 4
Park it if the check engine light is flashing or the engine is shaking. A flashing light means misfires severe enough to damage the catalytic converter and in extreme cases cause an exhaust fire. If the light is steady and the misfire is mild, drive only as far as needed to get it diagnosed, gently and without heavy loads.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0300 usually means on a Subaru
On older Subaru EJ25 engines, head gasket leaks are well documented, most often as external seepage. A leak that progresses can cause coolant loss and overheating. On newer FB engines, plugs and coils are more typical.
Most likely causes on Subaru vehicles
- Spark plugs (harder access on boxer engines)
- Coils
- Head gasket problems on older EJ25 (less common as a misfire cause)
- Vacuum leak
Order reflects cost and likelihood in general; your vehicle may differ. Confirm with testing before buying parts.
Subaru specific tips
- Watch coolant level and temperature.
- Plug changes on boxer engines take longer.
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Spark plugs, full set | $20 to $120 | 0.5 to 2.5 h | $20 + 0.5 × $110 = $75 $120 + 2.5 × $190 = $595 |
| Vacuum hose or intake gasket | $10 to $120 | 0.5 to 2.5 h | $10 + 0.5 × $110 = $65 $120 + 2.5 × $190 = $595 |
| Ignition coil, one | $30 to $150 | 0.2 to 1.0 h | $30 + 0.2 × $110 = $52 $150 + 1.0 × $190 = $340 |
| Fuel pump | $120 to $600 | 1.5 to 3.5 h | $120 + 1.5 × $110 = $285 $600 + 3.5 × $190 = $1,265 |
Costs are generic for this code; parts and labor on some Subaru models may run higher.
Watch a repair video
How to Fix a Random Engine Misfire in Your Car (Code P0300) (Scotty Kilmer). Third-party video, loads from YouTube (privacy-enhanced mode) only when you press play. Procedures vary by vehicle. Search YouTube for “P0300 Subaru fix” videos.
Repair manuals
Step-by-step service manuals for Subaru with torque specs and wiring diagrams:
Haynes manuals for Subaru Chilton manuals
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Check Subaru recalls
Enter your VIN at the NHTSA recall lookup before paying for repairs.
FAQ
Is a Subaru misfire always a head gasket?
No. Start with plugs and coils.
Read the full P0300 guide or more Subaru check engine notes.