P0300critical severityPowertrain
Random/Multiple Cylinder Misfire Detected
on 2015-2019 Subaru Legacy 2.5L H4 · AWD
What this code means
The PCM has detected misfires occurring in multiple cylinders randomly. This is different from a single-cylinder misfire and often points to a system-wide issue.
Symptoms
- Check Engine Light (flashing if severe)
- Rough idle
- Vibration
- Loss of power
- Hesitation
- Poor fuel economy
- Possible catalyst damage
Common causes
- Vacuum leak
- Low fuel pressure
- Faulty spark plugs (all)
- Ignition coil pack failure
- EGR valve stuck open
- Low compression (multiple cylinders)
- Wiring harness issue
- MAF sensor problem
Diagnostic steps
- Check for vacuum leaks (smoke test)
- Test fuel pressure
- Inspect spark plugs
- Test ignition coils
- Check fuel injectors
- Test compression
- Check MAF sensor
- Monitor fuel trim values
Repair notes
Start with spark plugs and vacuum leaks. Flashing CEL means severe misfire - stop driving to protect catalytic converter.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1