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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shock.

2. Inspect and Replace Spark Plugs

• Sub-steps:
  1. Remove the engine cover if applicable.
  2. Use a socket wrench to remove the spark plug wires or ignition coils.
  3. Use a spark plug socket to remove the spark plugs.
  4. Inspect the condition of the spark plugs. Replace any that show signs of wear or improper gap (use OEM recommended spark plugs).
  5. Install the new spark plugs and torque them to the manufacturer’s specifications (typically around 13-15 lb-ft).

3. Test and Replace Ignition Coils (if necessary)

• Sub-steps:
  1. Use a multimeter to test the resistance of each ignition coil.
  2. If any coils show outside of manufacturer specifications, replace them with new coils.
  3. Reinstall the ignition coils and ensure they are securely connected.

4. Clean or Replace Fuel Injectors

• Sub-steps:
  1. If injectors are clogged, use a fuel injector cleaner or remove them for ultrasonic cleaning.
  2. Replace any damaged or leaking injectors with OEM replacements.
  3. Reinstall the fuel rail and ensure all connections are tight.

5. Address Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum lines for cracks or disconnections.
  2. Replace any damaged vacuum lines.
  3. If no visible damage is found, use a smoke machine to detect hidden leaks.

6. Verify Fuel Pressure

• Sub-steps:
  1. Connect a fuel pressure gauge to the Schrader valve on the fuel rail.
  2. Turn the ignition to the "ON" position without starting the engine and check fuel pressure.
  3. Compare readings to manufacturer specifications; replace the fuel pump if pressure is low.