how to fix P0303 misfire code on Honda Accord 8th Generation (2008-2012)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative terminal of the battery to ensure safety.
• Tools Required: OBD-II scanner, socket set, torque wrench, spark plug socket, compression tester, fuel injector cleaner.

2. Replace Spark Plug

1. Locate the spark plug for cylinder 3 (typically the middle plug on the side of the engine).
2. Remove the ignition coil by unscrewing the retaining bolts and disconnecting the electrical connector.
3. Use a spark plug socket to remove the old spark plug.
4. Inspect the new spark plug for correct gap (0.044 inches) and install it using the spark plug socket.
5. Reattach the ignition coil and ensure it is securely fastened.

3. Inspect and Replace Ignition Coil

1. If the misfire persists after replacing the spark plug, remove the ignition coil from cylinder 3.
2. Swap the ignition coil with another cylinder (e.g., cylinder 1).
3. Clear the codes and take the vehicle for a test drive to see if the misfire code follows the ignition coil.
4. If the code shifts to the cylinder with the swapped coil, replace the faulty ignition coil.

4. Fuel Injector Cleaning and Replacement

1. If the misfire persists, check the fuel injector for cylinder 3.
2. Disconnect the fuel injector wiring harness and remove the injector.
3. Clean the injector using a fuel injector cleaner or replace it with a new one if cleaning doesn't resolve the issue.
4. Reinstall the injector and reconnect the wiring harness.

5. Compression Test

1. If all previous steps do not resolve the misfire, perform a compression test on cylinder 3.
2. Remove the spark plug and attach the compression tester to the spark plug hole.
3. Crank the engine and note the compression reading; it should be between 180-200 psi.
4. If the compression is low, further mechanical repairs may be needed, such as a head gasket replacement.