Cylinder 3 misfire
What P0303 means
Your car's computer set P0303: Cylinder 3 misfire. It belongs to the ignition system and misfire group of codes. It is a generic code, so it means the same thing on every make. The check engine light usually comes on once the fault has been seen on two drives in a row. Until then it shows up as a pending code.
Can I keep driving? If the check engine light is flashing, slow down and stop driving soon. A bad misfire can overheat and ruin the catalytic converter.
Common causes
- Worn spark plug in that cylinder
- Failing ignition coil (swap it with another cylinder to see if the misfire moves)
- Clogged or leaking fuel injector
- Low compression in that cylinder
Fix the cheapest, most likely cause first. Clearing the code without a repair only turns the light off until the fault comes back.
Check it yourself
Clear the code, swap the coil with a neighbouring cylinder, drive, and read codes again. If the cylinder number follows the coil, the coil is bad.
Torque Deck reads P0303 with a cheap Bluetooth OBD2 adapter. It also shows the freeze frame (engine conditions at the moment the code set) and the live data you need to narrow it down.
Parts
Parts most often replaced for P0303: spark plugs and ignition coils. Confirm the cause first, and match the part to your exact engine.
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Related codes
This page explains what the code usually means. It is not a diagnosis of your car. When in doubt, ask a mechanic.