P0300 — Random misfire across multiple cylinders — engine shakes at idle, stumbles under load, loses power, Check Engine light on solid or flashing
What it means
Common causes
- Worn or oil-fouled spark plugs — typical at 30–60K km with cheap plugs
- One or more failing ignition coils — common on VAG, Toyota, Nissan past 100K km
- Vacuum leak: cracked intercooler pipe, PCV valve, split vacuum lines
- Poor cylinder compression — worn rings, burnt valves, stretched timing chain
- Clogged or failing fuel injectors — especially on diesels and GDI engines
- Bad fuel — water, excess ethanol, low octane from a sketchy station
- Clogged exhaust or worn cat — back-pressure disrupts combustion
How to diagnose
- 01
Read all stored and pending codes with an OBD-II adapter — get the full picture, not just the one code.
- 02
Capture freeze-frame data (RPM, coolant temperature, engine load) at the exact moment the code triggered.
- 03
Inspect the named subsystem with our app's AI explanation — get vehicle-specific causes for your make, model and year.
Common patterns on specific vehicles
- Ford EcoBoost 1.5/1.6
On EcoBoost engines, P0300 is a bad ignition coil in ~60% of cases. Swap coils cylinder-to-cylinder — if the code follows, that's your coil.
- BMW N54/N55
On N54/N55 P0300 usually means cracked injectors (index-based recall) or HPFP. Check freeze frame during cold-start.
Empirical mechanic observations. Your case may differ — use as a starting hypothesis, not a diagnosis.
Decode P0300 on your actual car
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