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

Solution

1. Preparation

• Gather Tools and Parts: Collect an OBD-II scanner, socket set, fuel pressure gauge, compression tester, and any necessary replacement parts (spark plugs, ignition coils, etc.).
• Safety Precautions: Disconnect the negative battery terminal to prevent electrical shorts. Allow the engine to cool completely before starting work.

2. Inspect and Replace Ignition Components

• Remove Engine Cover (if applicable):

  • Use a socket set to unbolt the engine cover.
  • Carefully lift it off and set it aside.

• Check Spark Plugs:

  • Remove each spark plug using a spark plug socket.
  • Inspect for wear, fouling, or damage. Replace if necessary with OEM or equivalent spark plugs.

• Inspect Ignition Coils:

  • Disconnect electrical connectors from each ignition coil.
  • Unbolt the ignition coils and remove them.
  • Visually inspect for cracks or damage, and replace any faulty coils.

3. Fuel System Check

• Test Fuel Pressure:
  • Connect the fuel pressure gauge to the fuel rail.
  • Turn the ignition to the "ON" position (do not start) and check the pressure reading against manufacturer specifications.
  • If pressure is low, inspect the fuel pump and filter for issues; replace as needed.

4. Vacuum and Compression Check

• Inspect for Vacuum Leaks:

  • Start the engine and listen for hissing sounds around vacuum lines and the intake manifold.
  • Use a smoke machine or carb cleaner to detect leaks.

• Perform Compression Test:

  • Remove spark plugs and insert the compression tester into the spark plug hole of each cylinder.
  • Crank the engine and record the compression readings. Compare against manufacturer specifications.

5. Reassembly

• Reinstall Components:
  • Replace spark plugs and ignition coils, ensuring proper torque specifications are followed (typically 15-20 ft-lbs for spark plugs).
  • Reattach the engine cover if removed, ensuring all bolts are secured.

6. Final Checks

• Reconnect Battery:

  • Reattach the negative battery terminal.

• Clear Codes:

  • Use the OBD-II scanner to clear any diagnostic trouble codes.

• Test Drive:

  • Conduct a test drive to ensure the issue is resolved and monitor for any reoccurring codes.