P0300 on a 2022 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 2022 Subaru Outback

Ranked from 456 NHTSA owner complaints filed for this vehicle.

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1
Rod-bearing/bottom-end wear from low oil pressure
High severity
Two owners report an engine knock developing (one following a failed auto-restart, one during highway driving with the oil pressure light on) that was diagnosed as needing a replacement engine -- knock like this is commonly preceded by a rough-running misfire.
Reported in 2 NHTSA complaints
2
Valvetrain failure (broken intake valve)
High severity
One owner's engine teardown found a broken intake valve that punched a piston, an abrupt loss-of-compression event that would register as a severe misfire just before total failure.
Reported in 1 NHTSA complaint
Parts:intake valve piston
3
Worn or fouled spark plugs
Low severity
Standard misfire cause; check gap/wear against the service interval.
Common cause
Parts:spark plugs
4
Failing ignition coil
Medium severity
A weak coil causes an intermittent misfire on that cylinder; swap coils between cylinders to confirm.
Common cause
Parts:ignition coil
5
Clogged or leaking fuel injector
Medium severity
An injector delivering too little or dribbling fuel unbalances that cylinder's mixture.
Common cause
Parts:fuel injector
6
Vacuum/intake leak
Medium severity
Unmetered air leans out one or more cylinders, especially noticeable at idle; find with a smoke test.
Common cause
7
EGR valve fault
Low severity
Excess or stuck-open EGR flow dilutes the intake charge and causes a rough idle/misfire.
Common cause
Parts:EGR valve

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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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Matching symptoms

Car Runs Rough Flashing Check Engine Light