P0303 — Cylinder 3 Misfire Detected

Diagnostic checks and likely repair paths for a cylinder 3 misfire.

What It Means

The powertrain control module detected a misfire on cylinder 3.

Common Causes

• Faulty spark plug
• Faulty ignition coil
• Fuel injector issue
• Compression problem
• Vacuum leak near affected cylinder
• Coolant intrusion or head gasket issue

Quick Checks

• Inspect spark plug condition
• Swap ignition coil with another cylinder if applicable
• Inspect injector connector and function
• Check compression
• Look for coolant loss or signs of internal leak