how to fix P0300 misfire code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Replace Spark Plugs

• Sub-steps:
  1. Remove the engine cover (if applicable) using a socket set.
  2. Disconnect the ignition coils by unplugging the electrical connectors.
  3. Remove the ignition coils by unscrewing them from the cylinder head.
  4. Remove the old spark plugs using a spark plug socket.
  5. Inspect the old spark plugs for wear and gap consistency; replace if worn or damaged.
  6. Install new spark plugs with the correct gap (typically 0.043 inches for this model).
  7. Reinstall ignition coils and connect the electrical connectors.

3. Replace Ignition Coils (if necessary)

• Sub-steps:
  1. If any ignition coil showed signs of failure during inspection, replace it.
  2. Remove the faulty ignition coil from the cylinder head.
  3. Install the new ignition coil and reconnect the electrical connector.

4. Inspect and Clean Fuel Injectors

• Sub-steps:
  1. Remove the fuel rail from the engine (ensure to relieve fuel pressure first).
  2. Detach the fuel injectors from the rail.
  3. Clean the injectors using a fuel injector cleaning kit or replace if clogged.
  4. Reinstall the fuel injectors onto the rail and reinstall the fuel rail.

5. Check for Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum lines for cracks, wear, or disconnections.
  2. Use a smoke machine or carburetor cleaner to identify leaks while the engine is running.
  3. Replace any damaged vacuum lines.

6. Final Assembly

• Sub-steps:
  1. Reinstall any components removed during the repair.
  2. Reconnect the negative battery terminal.
  3. Start the engine and monitor for smooth operation.