how to fix P0300 random misfire code in Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, fuel pressure gauge, inspection mirror, flashlight.
• Safety Warnings: Disconnect the battery before working on electrical systems; allow the engine to cool before beginning repairs.

2. Replace Spark Plugs

• Remove the engine cover (if applicable).
• Disconnect the negative battery terminal.
• Remove the spark plug wire or ignition coil from each cylinder.
• Use a socket wrench to unscrew and remove the spark plugs.
• Inspect the old plugs for wear; replace with new plugs (OEM recommended).
• Reinstall the spark plugs and secure them to the specified torque (typically 13-15 ft-lbs).
• Reconnect the ignition coils or spark plug wires.

3. Test and Replace Ignition Coils (if necessary)

• Use a multimeter to test the primary and secondary resistance of each ignition coil according to specifications (typically around 0.4-2.0 ohms for primary).
• If a coil is defective, remove it by unbolting and disconnecting the electrical connector.
• Replace with a new ignition coil, securing it with the appropriate torque (10-12 ft-lbs).

4. Clean or Replace Fuel Injectors

• Perform a fuel pressure test to ensure injectors are delivering proper fuel pressure (typically 30-50 psi).
• If pressure is low, consider cleaning the injectors with a fuel injector cleaner or replacing them.
• To clean, remove the fuel rail, disconnect the injectors, and soak them in a cleaning solution per manufacturer instructions.
• Reinstall the fuel injectors and rail, ensuring all connections are secure.

5. Inspect and Repair Vacuum Leaks

• Visually inspect all vacuum hoses connected to the intake manifold for cracks or disconnections.
• Use an inspection mirror and flashlight to check hard-to-see areas.
• Replace any damaged hoses and ensure all connections are tight.