P0300 on a 2019 Subaru Crosstrek
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 2019 Subaru Crosstrek
Ranked from 281 NHTSA owner complaints filed for this vehicle.
- 1
Ignition coil pack failure (NHTSA Campaign WRE-21 coil defect)
High severityMultiple owners document coil packs shorting internally, blowing the ignition coil fuse, and producing a documented cylinder misfire (one shop explicitly scanned P0304) - this is a well-evidenced, vehicle-specific pattern, including a case where a coil pack caught fire even after the recall repair.
Reported in 6 NHTSA complaintsParts:ignition coil - 2
Oil intrusion into the spark plug well fouling the plug
Medium severityOne owner found the spark plug coil boot leaking oil directly onto the spark plug, which fouls the plug and disrupts spark.
Reported in 1 NHTSA complaint - 3
Worn spark plugs
Low severityStandard misfire cause; worn or improperly gapped plugs produce a weak spark under load.
Common causeParts:spark plugs - 4
Clogged or leaking fuel injector
Medium severityA dirty or dribbling injector disrupts the air/fuel charge in that cylinder, producing a repeatable misfire.
Common causeParts:fuel injector - 5
Vacuum or intake leak
Medium severityUnmetered air entering downstream of the throttle leans a cylinder enough to misfire.
Common cause - 6
Low cylinder compression (worn rings or valves)
High severityMechanical wear reducing compression in a cylinder produces a persistent misfire that ignition parts alone won't fix.
Common cause - 7
EGR valve/passage fault
Low severityExcess EGR flow at idle or light throttle can disrupt combustion in a cylinder enough to register as a misfire.
Common causeParts: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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