how to fix P0300 error code on Toyota Highlander XU70 (2020-Present)

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 short circuits.

2. Inspect and Replace Spark Plugs

• Remove the ignition coil covers using a socket set.
• Disconnect the electrical connectors from the ignition coils.
• Remove the ignition coils from the spark plugs.
• Unscrew and pull out the spark plugs using a spark plug socket.
• Inspect the old spark plugs; replace any that are worn or damaged.
• Install new spark plugs, ensuring they are gapped correctly as per manufacturer specifications (typically around 0.043 inches for the Highlander).
• Reinstall the ignition coils and connect the electrical connectors.

3. Check and Replace Ignition Coils (if necessary)

• If the ignition coils were found faulty during inspection, remove the faulty coils.
• Install new ignition coils in the same order they were removed.
• Ensure all connections are secure and the coils are seated properly.

4. Inspect and Clean Fuel Injectors

• If fuel injectors were suspected, remove them from the fuel rail.
• Clean the injectors using a fuel injector cleaning kit or replace them if they are clogged.
• Reinstall the cleaned or new fuel injectors ensuring seals are intact.

5. Check and Repair Vacuum Leaks

• Inspect all vacuum hoses for cracks or loose connections.
• Replace any damaged hoses and ensure all connections are tight.
• Use a smoke machine or carburetor cleaner to test for leaks in the intake manifold.

6. Perform Compression Test (if necessary)

• If misfire persists, perform a compression test on all cylinders.
• If compression is low in any cylinder, further investigation is needed for potential internal engine repairs (valve issues, piston rings, etc.).