how to fix P0300 misfire code in Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, multimeter, fuel pressure gauge, compression tester, vacuum gauge.
• Disconnect the negative battery terminal to avoid electrical shorts.
• Gather necessary replacement parts based on diagnostic findings.

2. Inspect and Replace Spark Plugs

• Remove the ignition coils by unscrewing the bolts and disconnecting the electrical connectors.
• Take out the spark plugs using a spark plug socket and inspect for wear or damage.
• Replace spark plugs with OEM or equivalent parts. Torque to manufacturer specifications (typically 13 ft-lbs).
• Reinstall ignition coils and reconnect electrical connectors.

3. Inspect and Replace Ignition Coils

• If misfire persists after spark plug replacement, test ignition coils with a multimeter for resistance.
• If defective, remove the faulty ignition coil by unscrewing the mounting bolt and disconnecting the connector.
• Install new ignition coils, ensuring they are seated properly. Torque to manufacturer specifications.

4. Check Fuel System

• Connect the fuel pressure gauge to the fuel rail.
• Turn the ignition to the "ON" position (do not start) and check for proper fuel pressure (typically 50-60 psi).
• If pressure is low, inspect the fuel pump, filter, and injectors for issues. Replace as necessary.

5. Inspect for Vacuum Leaks

• Use a vacuum gauge to check for leaks in the intake system.
• If a leak is detected, visually inspect hoses and gaskets for cracks or damage. Replace any faulty components.

6. Perform Compression Test

• Remove spark plugs and insert the compression tester into the spark plug holes.
• Crank the engine and record compression readings for each cylinder. Compare to manufacturer specifications (typically around 150-200 psi).
• If any cylinder shows significantly lower compression, investigate further for potential head gasket issues or valve problems.