What does code P0303 mean?

P0303: Cylinder 3 Misfire Detected

Severity: high

What it means: The engine computer counted misfires on cylinder 3, meaning that cylinder isn't burning its fuel properly.

Safe to drive? Only briefly, and gently, if the light is steady. Don't drive if the check-engine light is flashing, because unburned fuel can overheat and destroy the catalytic converter.

Common symptoms

Rough idle or shaking
Hesitation or loss of power
Flashing check-engine light under load
Worse fuel economy

Likely causes, ranked

Worn spark plug or failing ignition coil on that cylinder$218–$400DIY
CarMD 2024 national averages: ignition coil(s) about $218, coils plus spark plugs about $400
Fuel injector clogged or not firing$464Shop
CarMD 2024 national average about $464
Vacuum leak near that cylinderShop
Low compression (valve, ring or head gasket problem)Shop

Vehicle-specific notes

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
2015–2018 Ford Edge: 2.0L EcoBoost coolant leaking into the cylinders causes cold misfires. Ford's bulletin calls for a long block replacement. Read the full answer · Source

What it means: The engine computer counted misfires on cylinder 3, meaning that cylinder isn't burning its fuel properly.

Severity: High. Safe to drive? Only briefly, and gently, if the light is steady. Don't drive if the check-engine light is flashing, because unburned fuel can overheat and destroy the catalytic converter.

DIY or shop?

Swap the coil with a neighboring cylinder to see if the misfire follows it, a common DIY test. Compression and injector testing are shop jobs.

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.