how to diagnose P0300 random misfire code in Toyota Highlander XU70 (2020-Present)?

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Ensure the vehicle is in a safe, well-ventilated area.

2. Inspect Ignition Components

• Remove engine cover (if applicable) using a socket set.
• Check spark plugs:
  • Remove each spark plug using a spark plug socket.
  • Inspect for excessive wear, carbon buildup, or damage.
  • Replace spark plugs if worn beyond specifications (usually 0.024-0.028 inches gap).
• Check ignition coils:
  • Disconnect electrical connectors and remove bolts securing each coil.
  • Visually inspect for cracks or corrosion.
  • Replace any faulty ignition coils.

3. Fuel System Inspection

• Check fuel pressure:
  • Connect a fuel pressure gauge to the fuel rail.
  • Start the engine and observe pressure; it should be within the manufacturer’s specifications (typically 50-60 psi).
  • Replace the fuel pump or filter if pressure is low.

4. Vacuum Leak Inspection

• Check vacuum hoses:
  • Inspect all hoses for cracks or disconnections.
  • Use a smoke machine to pressurize the intake system and locate leaks.
  • Replace any damaged hoses.

5. Compression Test

• Perform compression test:
  • Remove spark plugs.
  • Insert a compression gauge into each cylinder and crank the engine.
  • Record compression readings; they should be within the manufacturer’s specified range (usually around 190-210 psi).
  • Address any low compression issues by checking piston rings or valves.