The P0303 diagnostic trouble code (DTC) is an OBD-II code stored by your vehicle's Engine Control Unit (ECU) when it detects cylinder 3 misfire detected. This code is part of the Engine Misfires system. When your check engine light comes on and a scan tool reads P0303, it means your vehicle needs attention in this area.
OBD-II codes starting with P0 are generic powertrain codes defined by the SAE standard, meaning P0303 has the same basic definition regardless of vehicle make or model. However, the specific causes and repair procedures can vary between manufacturers.
With a P0303 code, you should address this issue as soon as possible. Continued driving may cause damage to your catalytic converter, engine, or other components. If your check engine light is flashing, pull over safely and have the vehicle towed. A flashing light means active misfires that can cause immediate catalytic converter damage.