how to fix P0304 code on Honda Accord 8th Generation (2008-2012)

Learn how to diagnose and fix P0304 cylinder 4 misfire in Honda Accord 2008-2012. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface, and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shocks.

2. Replace Spark Plug

• Remove the ignition coil cover if necessary.
• Disconnect the wiring harness from the ignition coil on cylinder 4.
• Unscrew the ignition coil and remove it from the cylinder head.
• Use a spark plug socket to remove the spark plug from cylinder 4.
• Install a new spark plug, ensuring it is gapped correctly (typically 0.044 inches for Honda).
• Reinstall the ignition coil and reconnect the wiring harness.

3. Test or Replace Fuel Injector

• Disconnect the fuel injector wiring harness on cylinder 4.
• Remove the fuel injector from the intake manifold.
• Test the injector's resistance with a multimeter (specs vary by model).
• If the injector is faulty, replace it with a new one. If functional, clean the injector using a fuel injector cleaner.

4. Check Ignition Coil

• Swap the ignition coil from cylinder 4 with another cylinder (e.g., cylinder 1).
• Clear the codes and run the engine to see if the misfire code follows the ignition coil.
• If it does, replace the ignition coil; if not, the coil may be fine.

5. Compression Testing

• Insert a compression gauge into the spark plug hole of cylinder 4.
• Crank the engine to take the reading.
• Compare the reading to the manufacturer’s specifications (typically 180-220 psi).
• If the compression is low, further investigation into valve or piston issues may be required.