how to fix the P0300 code on my Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative battery terminal to prevent electrical shock.
• Allow the engine to cool before starting work.

2. Inspect and Replace Ignition Components

• Tools Required: Socket set, torque wrench, ratchet, pliers.
• Inspect spark plugs for wear. If worn or fouled, remove and replace them.
  • Remove the ignition coil by unscrewing the retaining bolts.
  • Pull the coil out gently to avoid damaging the connector.
  • Replace the old spark plug with a new one, ensuring it is gapped correctly (usually 0.044 inches for Toyota).
  • Reinstall the ignition coil and torque it to the manufacturer’s specifications (typically 7-10 ft-lbs).

3. Check Fuel System

• Tools Required: Fuel pressure gauge.
• Connect the fuel pressure gauge to the fuel rail Schrader valve.
• Turn the ignition key to the “ON” position without starting the engine to check fuel pressure. Compare the reading against manufacturer specifications (usually around 30-50 psi).
• If the pressure is low, inspect the fuel filter and fuel pump for issues and replace if necessary.

4. Inspect Vacuum Lines and MAF Sensor

• Tools Required: Visual inspection tools.
• Inspect all vacuum hoses for cracks or disconnections, especially around the intake manifold. Replace any damaged hoses.
• Remove the MAF sensor and clean it using MAF sensor cleaner.
• Reinstall the MAF sensor securely to prevent air leaks.

5. Compression Test

• Tools Required: Compression tester.
• Remove the spark plugs.
• Insert the compression tester into the first cylinder and crank the engine.
• Record the compression reading and repeat for each cylinder. Compare readings to manufacturer specifications (typically 180-200 psi).
• Replace any cylinder with low compression due to internal engine issues.