P0300 on a 2015 Subaru Forester
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 2015 Subaru Forester
Ranked from 613 NHTSA owner complaints filed for this vehicle.
- 1
Excessive Oil Consumption / Internal Engine Wear
High severityThe FB25 engine in this generation is known for excessive oil consumption, leading to low oil levels, piston ring wear, and loss of compression. This can cause misfires (P0300) and stalling.
Reported in 6 NHTSA complaints - 2
Cam Carrier / Front Cover Oil Leak
Medium severityOil leaking from the cam carrier or front cover can contaminate the wiring harness, O2 sensors, and VVT solenoids, leading to erratic engine operation and random misfires.
Reported in 1 NHTSA complaint - 3
Faulty Mass Air Flow (MAF) Sensor
Medium severityA failing MAF sensor can cause incorrect air/fuel mixture calculations, leading to stalling, hesitation, and random misfires.
Reported in 1 NHTSA complaint - 4
Ignition Coil Failure
Medium severityFailing ignition coils are a standard cause of P0300. Some complaints mention a recall or replacement of coils causing starting/running issues.
Reported in 1 NHTSA complaint - 5
Blown Head Gasket
High severityCoolant leaking into the combustion chamber or loss of compression due to a failed head gasket can cause severe misfires and engine failure.
Reported in 1 NHTSA complaint - 6
Low Fuel Pressure / Fuel Delivery Issue
Medium severityA failing fuel pump, clogged fuel filter, or moisture in the fuel lines can starve the engine of fuel, causing hesitation, stalling, and misfires.
Reported in 1 NHTSA complaint - 7
Worn Spark Plugs
Low severityWorn or fouled spark plugs are a primary generic cause for random/multiple cylinder misfires (P0300).
Common cause - 8
Vacuum Leak
Medium severityUnmetered air entering the intake manifold leans out the air/fuel mixture, causing random misfires across multiple cylinders.
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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