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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety during repairs.
• Allow the engine to cool before beginning work.

2. Inspect and Replace Spark Plugs

• Tools Required: Socket set, spark plug socket, torque wrench.
• Remove the ignition coil connectors and bolts.
• Carefully pull out the ignition coils.
• Remove spark plugs using the spark plug socket.
• Inspect each spark plug for wear, carbon buildup, or damage.
• Replace with OEM-spec spark plugs, torquing to manufacturer specifications (typically around 13 lb-ft).

3. Check and Replace Ignition Coils

• Tools Required: Socket set, multimeter (for testing).
• Visually inspect ignition coils for cracks or damage.
• Use a multimeter to test the resistance of each coil (check manufacturer specs).
• Replace any faulty ignition coils with OEM parts.

4. Inspect and Clean Fuel Injectors

• Tools Required: Fuel injector cleaning kit or professional service.
• Remove the fuel rail if necessary (ensure to relieve fuel pressure before disconnecting).
• Use a fuel injector cleaning kit to clean or replace clogged injectors.
• Reinstall the fuel rail and ensure proper sealing.

5. Perform Engine Compression Test

• Tools Required: Compression tester.
• Remove spark plugs, and insert the compression tester into each cylinder.
• Crank the engine several times and record the compression readings.
• Compare results against manufacturer’s specifications; replace engine components as necessary if low compression is found.

6. Inspect Air Intake System

• Tools Required: Visual inspection tools.
• Check for any vacuum leaks in hoses connected to the intake manifold.
• Inspect the air filter for blockages and replace if necessary.