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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical short circuits during repairs.
• Allow the engine to cool down before working.

2. Inspect and Replace Spark Plugs

• Tools Required: Socket set, spark plug socket, torque wrench.
• Remove the ignition coil cover if applicable.
• Disconnect the ignition coil connectors and remove the coils.
• Use a spark plug socket to remove the spark plugs.
• Inspect the spark plugs for wear and carbon buildup; replace if necessary.
• Install new spark plugs, ensuring they are torqued to the manufacturer's specifications (typically around 13-16 lb-ft).
• Reinstall the ignition coils and connectors.

3. Check and Replace Ignition Coils

• Tools Required: Socket set, multimeter (for testing).
• Test each ignition coil using a multimeter according to the manufacturer's specifications.
• If any coil fails the test, remove the faulty coil and replace it with a new one.
• Reconnect the coil connectors and ensure they are seated properly.

4. Inspect and Clean Fuel Injectors

• Tools Required: Fuel injector cleaning kit or replacement injectors.
• If fuel injector issues are suspected, remove the fuel rail to access the injectors.
• Inspect the injectors for clogs; clean using a fuel injector cleaning kit or replace if necessary.
• Reinstall the fuel rail and ensure all connections are secure.

5. Check for Vacuum Leaks

• Tools Required: Smoke machine or carburetor cleaner.
• With the engine running, use a smoke machine to identify any vacuum leaks or spray carburetor cleaner around potential leak points.
• Repair or replace any damaged hoses or gaskets found during inspection.

6. Verify Engine Compression

• Tools Required: Compression tester.
• Remove spark plugs and insert the compression tester into each cylinder.
• Crank the engine and record the compression readings; they should be within the manufacturer's specified range.
• If any cylinder has low compression, further diagnosis may be needed for internal engine issues.