P0300 on a 2013 Subaru Outback
P0300 is a generic OBD2 powertrain code for random or multiple cylinder misfire. Unlike P0301 through P0308, it does not point to one specific cylinder, so the cause can be ignition, fuel, air, sensor, or mechanical.
Not your vehicle? See general P0300 info.
Most common causes on the 2013 Subaru Outback
Ranked from 295 NHTSA owner complaints filed for this vehicle.
- 1
Excessive oil consumption / Piston ring failure
High severityLook for low oil levels, heavy oil burning, or fouled spark plugs. Confirmed by an oil consumption test or excessive oil deposits in the intake/throttle body.
Reported in 9 NHTSA complaints - 2
Defective valve springs
High severityLook for a broken valve spring causing a dropped valve and engine seizure. Confirmed by internal engine inspection and referencing TSB #10154425.
Reported in 1 NHTSA complaint - 3
Faulty spark plugs
Medium severityLook for worn or fouled spark plugs causing weak spark. Confirmed by visual inspection of the plug electrodes and gap.
Common cause - 4
Faulty ignition coils
Medium severityLook for cracked coil boots or internal coil failure. Confirmed by testing coil resistance or swapping coils to see if the misfire moves.
Common cause - 5
Vacuum leak
Medium severityLook for cracked or disconnected vacuum hoses causing a lean condition. Confirmed by a smoke test or listening for hissing sounds.
Common cause - 6
Fuel delivery issue (injectors or pump)
Medium severityLook for clogged fuel injectors or low fuel pressure. Confirmed by fuel pressure testing or injector flow testing.
Common cause
These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0300 on your car still needs shop confirmation before any repair.
Common symptoms
- Flashing or steady check engine light
- Rough idle
- Shaking under acceleration
- Loss of power
- Fuel smell from exhaust
What to check before replacing parts
Scan for cylinder-specific misfire codes
Look for: A companion P0301–P0308 pins the misfire to one cylinder — start there. P0300 with no cylinder code points at something hitting several at once: fuel pressure, a large vacuum leak, or timing.
Inspect the spark plugs and coils
Look for: Pull the plugs: black/sooty = rich, oily = oil intrusion, white/blistered = lean or overheating, cracked porcelain or an out-of-spec gap = replace. Then swap a coil to another cylinder — if a cylinder-specific code follows the coil, the coil is bad.
Check fuel trims for a vacuum leak
Look for: High positive short- and long-term trims (worst at idle, improving as RPM rises) mean unmetered air is getting in. Smoke-test the intake and listen for hissing.
Verify fuel pressure
Look for: Compare running/cranking pressure to the vehicle spec. Low or dropping pressure starves multiple cylinders and reads as a random misfire — suspect the pump, filter, or regulator.
Compression / leak-down test if ignition and fuel check out
Look for: A cylinder 15%+ below the others, or leak-down hissing from the intake (intake valve), exhaust (exhaust valve), or oil filler (rings), means the misfire is mechanical — not a swap-in part.
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