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

Solution

1. Preparation

• Gather all 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 shorts.

2. Inspect and Replace Spark Plugs

• Remove the engine cover if applicable using a socket set.
• Disconnect the ignition coils, and remove them using a socket wrench.
• Remove the spark plugs using a spark plug socket.
• Inspect the spark plugs for signs of wear or fouling; replace with OEM equivalent if necessary (Torque: approximately 13 lb-ft).
• Reinstall the ignition coils and reconnect the wiring harness.

3. Inspect and Replace Ignition Coils

• If any ignition coils were found defective during inspection, remove them as described in Step 2.
• Install the new ignition coils (ensure they are compatible with the vehicle model).
• Reconnect the ignition coils to the wiring harness securely.

4. Check Fuel System

• Connect a fuel pressure gauge to the fuel rail.
• Turn the ignition key to the "ON" position (do not start the engine) and check the fuel pressure; it should match the specifications (typically around 50-60 psi).
• If the pressure is low, inspect the fuel filter and replace if clogged.
• If necessary, clean or replace fuel injectors using an appropriate fuel injector cleaner.

5. Inspect Air Intake and Vacuum System

• Check the air intake hose for cracks or disconnections and replace if damaged.
• Inspect all vacuum hoses for leaks and replace any that are cracked or damaged.
• If applicable, clean the throttle body and mass airflow sensor with appropriate cleaning products.