What does code P0300 mean?

P0300: Random/Multiple Cylinder Misfire Detected

Severity: high

What it means: The engine computer is seeing misfires on more than one cylinder, or moving randomly between cylinders.

Safe to drive? Not recommended if the light is flashing. With a steady light, drive gently and get it checked soon.

Common symptoms

Rough running or shaking
Loss of power
Flashing check-engine light
Fuel smell from the exhaust

Likely causes, ranked

Worn spark plugs or ignition coils$218–$400DIY
CarMD 2024 national averages: ignition coil(s) about $218, coils plus spark plugs about $400
Vacuum leak or lean fuel mixtureShop
Low fuel pressure or dirty injectors$464Shop
CarMD 2024 national average about $464
Engine mechanical problem (compression, timing)Shop

Vehicle-specific notes

2011–2014 Ford F-150: 3.5L EcoBoost: misfire or stumble on hard acceleration after highway driving in humid weather. Ford's bulletin adds a revised deflector and PCM update, and checks the left catalytic converter if P0430 is set. Read the full answer · Source
2016–2018 Honda Civic: 1.5L turbo fuel/oil dilution. Honda's warranty extension covers these misfire and rich codes with a software update. Read the full answer · Source
2017–2019 Honda CR-V: 1.5L turbo fuel/oil dilution. Honda's warranty extension covers these misfire and rich codes with a software update. Read the full answer · Source

What it means: The engine computer is seeing misfires on more than one cylinder, or moving randomly between cylinders.

Severity: High. Safe to drive? Not recommended if the light is flashing. With a steady light, drive gently and get it checked soon.

DIY or shop?

Plugs and coils are often DIY. A misfire that won't stay fixed needs shop diagnosis.

Before you replace parts

Read all stored codes and freeze-frame data. Fix misfire, fuel or sensor codes before chasing emissions codes.
Check the simple things first: connectors, vacuum hoses, fluid levels and the gas cap.
Clear the code only after a repair, then confirm it stays off after a few drives.
Check your VIN for recalls and service bulletins.

Safety / mechanic note

Verify with a mechanic. This code can involve stalling, engine damage or loss of power. If the check-engine light is flashing, or the car stalls or runs badly, stop driving and have it inspected.