my Toyota Highlander XU70 (2020-Present) has a check engine light with code P0300

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal for safety.

2. Inspect and Replace Ignition Components

• Tools Required: Socket set, torque wrench, spark plug socket, dielectric grease.
• Remove the engine cover if applicable.
• Disconnect the ignition coils from the electrical connectors.
• Remove the ignition coils using the socket set and inspect for damage. Replace if necessary.
• Remove the spark plugs with a spark plug socket and inspect for wear or fouling.
  • If worn, replace with OEM spark plugs, ensuring the gap is set correctly.
• Apply dielectric grease to the terminals of the ignition coils before reinstalling.
• Reinstall the ignition coils and secure them with the torque wrench to the manufacturer’s specified torque value.

3. Check Fuel System

• Tools Required: Fuel pressure gauge, safety goggles.
• Locate the fuel pressure test port on the fuel rail.
• Attach the fuel pressure gauge and turn the ignition to the "ON" position without starting the engine.
• Check the fuel pressure reading against the manufacturer's specifications. If low, check for a faulty fuel pump or clogged fuel filter.
• Replace the fuel filter if necessary and ensure proper fuel flow.

4. Inspect Air Intake and Vacuum System

• Tools Required: Basic hand tools for hose clamps.
• Inspect the air intake duct for any cracks or loose connections.
• Check the Mass Air Flow (MAF) sensor for dirt or contamination. Clean with MAF cleaner if necessary.
• Examine all vacuum lines for leaks or damage. Replace any faulty hoses.

5. Perform Compression Test

• Tools Required: Compression gauge.
• Remove the spark plugs again to allow for easier access to the cylinders.
• Insert the compression gauge into the spark plug hole and crank the engine several times.
• Record the compression readings for each cylinder. If any cylinder shows low compression, diagnose further for potential issues such as valve problems or head gasket failure.