Summary
P0305 means the PCM detected repeated misfires in cylinder 5. This code only appears on 5+ cylinder engines (V6, V8, inline-5, inline-6). The diagnostic approach is the same as any single-cylinder misfire: check the spark plug, ignition coil, and fuel injector for cylinder 5. Use the coil-swap test — move cylinder 5's coil to another cylinder, clear codes, and drive. If the misfire follows, replace the coil ($20–$80).
Severity: Moderate to High — misfires damage catalytic converters
Safe to drive: Not recommended
Repair cost: $20–$500 depending on cause
DIY difficulty: Easy to Moderate
What does P0305 mean?
The PCM detected that cylinder 5 is misfiring beyond the acceptable threshold. On V6 and V8 engines, cylinder 5 is on the second bank (Bank 2 on most manufacturers). On inline-5 engines (Volvo, some Audi), it's the last cylinder. Confirm the cylinder numbering from your service manual — it varies by manufacturer.
If P0300 is also present, the misfire may affect additional cylinders. If only P0305, the problem is specific to cylinder 5's ignition, fuel, or compression.