P0304 Code: Cylinder 4 Misfire Detected

What does P0304 mean?

P0304 indicates Cylinder 4 is misfiring. Inspect the spark plug, ignition coil and injector for cylinder 4. When this code is set, the engine computer has detected a condition that falls outside its expected parameters for normal operation.

Common causes of P0304

The most frequent causes of a P0304 code fall into four categories:

• Component failure — worn sensors, failed relays, or aging parts that can no longer produce reliable signals.
• Wiring and connectors — corroded pins, chafed wires, or loose ground points that break the signal chain.
• Mechanical issues — vacuum leaks, exhaust leaks, or fuel delivery problems that affect the sensor readings.
• Software and calibration — occasional ECU glitches after battery disconnection or updates.

Run the AI-powered diagnostic tool below to get vehicle-specific causes, ranked by likelihood.

How to diagnose P0304

1. Read the full scan — any codes stored alongside P0304 usually point to the real cause.
2. Inspect the most commonly associated components for visible damage or wear.
3. Check wiring and connectors for corrosion or breaks.
4. Test with a multimeter or scope where relevant.
5. Confirm by clearing the code and driving a complete drive cycle.

How serious is P0304?

The severity depends on the underlying cause. In most cases, P0304 doesn't stop the vehicle running — but ignoring it can cause further damage, reduced fuel economy, and failure of a roadworthy or emissions inspection. Get it diagnosed within a few hundred kilometres.

Can I drive with P0304?

Short-term driving is usually fine. Avoid long trips or heavy loads until diagnosed — some underlying faults can escalate to expensive repairs if left unchecked.