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

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Ensure the engine is cool and disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Spark Plugs

• Tools Required: Socket set, ratchet, extension, spark plug gap tool.
• Remove the ignition coils by unclipping the electrical connectors and unscrewing the bolts.
• Carefully pull out the spark plugs using a spark plug socket.
• Inspect the spark plugs for wear; replace any that are damaged or fouled.
• Ensure new spark plugs are gapped according to manufacturer specifications (typically around 0.044 inches).
• Reinstall the spark plugs and ignition coils, ensuring to torque them to the manufacturer’s specification (usually around 13-16 ft-lbs).

3. Check and Replace Ignition Coils (if necessary)

• Tools Required: Socket set, multimeter (for testing).
• Test each ignition coil with a multimeter to ensure proper resistance values. If any coil is out of specification, replace it.
• Reinstall the new coils, ensuring all connections are secure.

4. Clean or Replace Fuel Injectors

• Tools Required: Fuel injector cleaning kit or replacement injectors, safety glasses.
• If injectors are clogged, clean them using a fuel injector cleaning kit following the manufacturer’s instructions.
• If injectors are faulty, replace them by disconnecting the fuel line and electrical connectors, removing the mounting bolts, and installing new injectors.

5. Inspect Vacuum Lines

• Visually inspect all vacuum lines for cracks, disconnections, or damage.
• Replace any damaged lines to ensure optimal engine performance.

6. Compression Test (if misfires persist)

• Tools Required: Compression tester.
• Remove the spark plugs, insert the compression tester into each cylinder, and crank the engine.
• Compare the compression readings to manufacturer specifications; if readings are low, further diagnosis is needed to determine the cause.