The P0303 diagnostic trouble code means the engine has a misfire on cylinder 3. In practice, drivers often notice a rough idle, reduced power, and a check engine light, among other signs.
What P0303 means
P0303 indicates a misfire in cylinder 3 detected by the engine control module. A misfire occurs when the air–fuel mixture in that cylinder fails to ignite reliably, causing the engine to run roughly and lose power. Causes can include a faulty spark plug, a bad ignition coil, a dirty or clogged fuel injector, low compression, vacuum leaks, or faulty wiring. Diagnosis typically involves inspecting ignition components, testing fuel delivery, and checking compression and timing.
Common symptoms
The following symptoms are commonly reported by drivers when P0303 is active. Not every symptom appears in every vehicle, and some may be caused by other problems.
- Rough idle or noticeable engine vibration at idle
- Engine misfire signs such as hesitating, stumbling, or coughing during acceleration
- Loss of power or reduced acceleration responsiveness
- Lower fuel economy and higher fuel consumption
- Check Engine Light (CEL) or Malfunction Indicator Light (MIL) on the dashboard
- Flashing CEL in cases of a severe misfire, potentially with stalling under load
- Unusual exhaust sounds or popping noises
These symptoms point to a misfire in cylinder 3 and warrant a diagnostic check of ignition, fuel delivery, and compression components to identify the root cause.
Summary
P0303 denotes a misfire in cylinder 3. Typical symptoms include a rough idle, hesitation or power loss, reduced fuel economy, and a lit check engine light. Prompt diagnosis helps prevent further engine damage and ensures proper repair of ignition or fuel delivery issues.