Severity: High
Can damage expensive parts or affect drivability. Limit driving and book promptly.
What P0300 means
The engine computer is counting misfires on more than one cylinder, or they move around. That usually points to something shared by all cylinders: fuel pressure, a vacuum leak, ignition supply or engine mechanical condition.
Symptoms
- Rough idle or shaking
- Flashing check engine light under load
- Loss of power or hesitation
- Fuel smell from the exhaust
Common causes
Most likely first
- 1Worn spark plugs
- 2Vacuum leak
- 3Low fuel pressure or weak pump
- 4Dirty MAF sensor causing lean running
- 5Engine mechanical (timing, compression)
- 6EGR valve stuck open
How we diagnose it
- Check misfire counters per cylinder in live data
- Swap the coil to another cylinder and see if the misfire follows
- Inspect plug condition and gap
- Check fuel trims for a lean condition
- Compression or leak-down test if ignition and fuel check out
Every vehicle sets codes under its own conditions. We check the factory diagnostic steps and service bulletins for your VIN, so the repair targets the actual cause.