Can I keep driving?
Avoid driving if the check engine light is flashing — unburned fuel can overheat and destroy the catalytic converter. A steady light: drive gently and book soon.
What it means
The engine computer counts misfires by watching crankshaft speed. P0300 means misfires are random or spread across cylinders; P0301–P0308 point to a specific cylinder (P0301 = cylinder 1, and so on).
Common symptoms
- Rough idle or shaking
- Flashing check engine light
- Hesitation or loss of power
- Worse fuel economy
- Fuel smell from the exhaust
Common causes
- Worn spark plugs
- Failing ignition coil
- Leaking or clogged fuel injector
- Carbon buildup on intake valves (direct-injection engines)
- Vacuum leaks
- Low compression (valves, rings, head gasket)
How we diagnose it
- Read freeze-frame data and misfire counters per cylinder
- Swap coils/plugs between cylinders to see if the misfire follows the part
- Check injector balance and fuel trims
- Compression or leak-down test when a mechanical cause is suspected
- Inspect intake valves for carbon on direct-injection engines
Where we see it most: BMW, Audi/VW (direct injection), Mercedes-Benz, MINI
A code points to the system that reported a problem, not the exact failed part. Replacing parts based on the code alone often wastes money — testing finds the real cause.