A misfire usually needs a check soon; if the check-engine light is flashing, stop when safe and switch off the engine.
Trouble codes · P0300
P0300 meaning
Random/Multiple Cylinder Misfire Detected
The same first verdict Car Assist shows from this code alone, before a diagnosis. The code does not tell the app whether the warning light is flashing.
What this code doesn’t tell you
A code says where the car noticed a problem. It does not prove which part failed, whether the fault is still present, or what repair this car needs. The engine, other codes, freeze frame and live readings matter.
Usual causes, most likely first
The order is a starting point across cars; the exact engine and its readings can change it.
- Worn spark plugs or ignition coils on petrol engines
- Intake leak or fuel delivery fault
- Injector or mechanical compression fault
What you can check
Keep the freeze frame and note whether shaking happens cold, at idle or under load. Usually a flashing check-engine light needs a stop when safe and the engine switched off; have the misfire checked.
Words the car uses
- Stored codes
- Faults the car has confirmed and saved. They help explain a check-engine light, but a code alone does not prove which part needs replacing.
- Freeze frame
- A snapshot of the engine's readings when a fault was recorded. It helps show the conditions that caused the fault, even if the car now seems fine.
- Readiness monitors
- The car's own checks of its emissions systems. An unfinished check means the car has not tested that system yet, so a clean code scan may miss a fault.
- Misfire
- A cylinder has failed to burn its fuel properly. It can cause shaking and loss of power; a flashing check-engine light usually means stop when safe and switch off the engine.
- Check-engine light (MIL)
- The engine warning light on the dashboard; MIL is its diagnostic name. A flashing light usually risks damage to the catalytic converter, so stop when safe and switch off the engine.
- Fuel trims (STFT and LTFT)
- How much the engine computer adds to or takes away from its planned fuel amount. STFT is the immediate adjustment and LTFT is the learned adjustment; B1 and B2 identify groups of cylinders, and large adjustments can point to an air or fuel problem.
Find out what’s causing yours
Car Assist reads your car through an OBD-II adapter and your iPhone. Its assistant uses the codes, freeze frame and live readings to work through the likely cause with you.