how to fix the P0304 code on my Honda Civic 9th Generation (2012-2015)

Solution

1. Preparation

• Gather tools and necessary parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool before starting work.

2. Inspect and Replace Spark Plug

• Tools Required: Socket set, spark plug socket, torque wrench
• Remove engine cover (if applicable).
• Disconnect the ignition coil connector and unscrew the ignition coil from cylinder 4.
• Remove the spark plug using a spark plug socket.
• Inspect the spark plug for wear or damage; replace it with a new one if necessary.
• Torque the new spark plug to the manufacturer's specification (typically around 13 lb-ft).
• Reinstall the ignition coil and reconnect the connector.

3. Inspect and Replace Ignition Coil

• If the spark plug is fine, proceed to inspect the ignition coil.
• Tools Required: Socket set
• Remove the ignition coil from cylinder 4.
• Test the ignition coil with a multimeter to ensure it is within specifications (check resistance).
• If faulty, replace the ignition coil with a new one and reinstall it.

4. Check Fuel Injector

• Tools Required: Fuel pressure gauge, basic hand tools
• Remove the fuel injector connector for cylinder 4.
• Test the injector resistance with a multimeter; it should match specifications.
• If faulty, replace the fuel injector, ensuring to use new O-rings.
• Reconnect the injector connector.

5. Compression Test

• Tools Required: Compression tester
• Remove the spark plug from cylinder 4.
• Insert the compression tester into the spark plug hole.
• Crank the engine and record the compression reading; it should be within the specified range (usually around 180-200 psi).
• If the reading is low, further diagnosis for internal engine issues is required.

6. Inspect for Vacuum Leaks

• Tools Required: Smoke machine or carburetor cleaner
• With the engine running, use a smoke machine to detect leaks in the intake system or spray carburetor cleaner around potential leak points.
• If the engine RPM changes, a vacuum leak is present and should be repaired.