how to fix P0303 misfire code on my Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather tools and parts needed.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool if it has been running.

2. Replace Spark Plug

• Sub-steps:
  • Remove the engine cover if necessary (use a socket set).
  • Disconnect the ignition coil connector from the spark plug.
  • Remove the ignition coil using a ratchet and socket.
  • Remove the spark plug using a spark plug socket.
  • Install the new spark plug, ensuring it is gapped correctly (typically 0.043 inches for many Toyota models).
  • Reinstall the ignition coil and connector.

3. Replace Ignition Coil (if faulty)

• Sub-steps:
  • If the ignition coil is found to be defective during testing, remove it (as described above).
  • Install the new ignition coil, ensuring it is seated properly.
  • Reconnect the ignition coil connector.

4. Inspect and Clean Fuel Injector (if needed)

• Sub-steps:
  • Remove the fuel rail if access is required.
  • Disconnect the fuel injector connector and remove the injector from the rail.
  • Clean the injector using a fuel injector cleaning kit or replace it if malfunctioning.
  • Reinstall the injector and reconnect the fuel rail.

5. Reassemble and Test

• Reconnect any components removed during the repair.
• Reconnect the negative battery terminal.
• Start the engine and observe for any check engine lights or misfires.