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

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the battery before starting any repairs.
• Ensure the vehicle is on a flat surface and secure it with wheel chocks.

2. Inspect and Replace Spark Plugs

• Sub-steps:
  1. Remove the engine cover (if applicable) using a socket set.
  2. Disconnect the ignition coil connectors and remove the coils.
  3. Remove the spark plugs using a spark plug socket.
  4. Inspect the spark plugs for wear, carbon buildup, or damage.
  5. Replace with OEM equivalent spark plugs, ensuring the gap is set to manufacturer specifications (typically around 0.044 inches).
  6. Reinstall spark plugs and ignition coils, reconnecting the connectors.

3. Test and Replace Ignition Coils

• Sub-steps:
  1. Use a multimeter to check the resistance of each ignition coil; compare readings to specifications.
  2. If any coils are out of spec, replace them with new OEM coils.
  3. Reinstall the ignition coils and ensure connectors are secure.

4. Check Fuel Injectors

• Sub-steps:
  1. Use a noid light to check for proper signal to each fuel injector while cranking the engine.
  2. If a noid light does not flash, inspect the wiring and connectors for damage.
  3. If the injectors are faulty, remove and replace them with OEM fuel injectors.

5. Inspect for Vacuum Leaks

• Sub-steps:
  1. Visually inspect all vacuum lines for cracks or disconnections.
  2. Use a smoke machine or carburetor cleaner to identify leaks by spraying around suspected areas.
  3. Repair or replace any leaking vacuum lines.

6. Measure Engine Compression

• Sub-steps:
  1. Remove spark plugs and disable the fuel injection system.
  2. Use a compression tester to measure the pressure in each cylinder.
  3. Record readings; if any cylinder is significantly lower than others, further investigation into mechanical issues is needed.