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

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, multimeter, compression tester.
• Safety Warnings: Disconnect the battery before working on electrical systems.

2. Inspect and Replace Spark Plugs

1. Remove the engine cover (if applicable) to access the ignition components.
2. Disconnect the ignition coils from the spark plugs.
3. Using a socket wrench, remove the spark plugs from each cylinder.
4. Inspect the spark plugs for wear, carbon buildup, or damage. Replace with OEM specifications if necessary.
5. Torque the new spark plugs to the manufacturer’s specifications (typically around 13-15 lb-ft).

3. Check and Replace Ignition Coils

1. After removing spark plugs, inspect the ignition coils for cracks or corrosion.
2. Test ignition coils with a multimeter to check for proper resistance (consult service manual for specific values).
3. Replace defective ignition coils with new OEM parts.
4. Reconnect the ignition coils back to the spark plugs.

4. Fuel System Inspection and Repair

1. Check the fuel pressure using a fuel pressure gauge; it should meet manufacturer specifications (usually around 50-60 psi).
2. Replace the fuel filter if it is clogged or has not been changed according to the maintenance schedule.
3. If the fuel pump is faulty, replace it according to manufacturer guidelines.

5. Vacuum Leak Inspection

1. Visually inspect all vacuum lines for cracks or disconnections.
2. Use a smoke machine or spray soapy water to locate any vacuum leaks in the intake manifold or hoses.
3. Repair or replace any damaged vacuum lines.

6. Compression Test

1. Remove all spark plugs and disable the fuel system to prevent flooding.
2. Insert the compression tester into the spark plug hole and crank the engine.
3. Record the compression values for each cylinder and compare them to the specifications (typically around 170-210 psi).
4. Address any cylinders that show significantly lower compression by checking for valve issues or mechanical failures.