how to fix P0300 code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, fuel pressure gauge, compression tester, vacuum gauge.
• Ensure the engine is cool before starting work.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Spark Plugs

1. Remove the engine cover if applicable.
2. Disconnect the ignition coils from each spark plug.
3. Using a socket set, carefully remove the spark plugs.
4. Inspect each spark plug for wear; replace any that are damaged or fouled.
5. Gap the new spark plugs according to manufacturer specifications.
6. Install new spark plugs and torque to the recommended value (usually around 13-15 lb-ft).
7. Reconnect the ignition coils.

3. Check and Replace Ignition Coils (if necessary)

1. If spark plugs are in good condition, inspect the ignition coils visually for cracks or damage.
2. Disconnect the wiring harness and remove the ignition coils using a socket set.
3. Install new ignition coils if any are found defective.
4. Torque the ignition coils to the manufacturer's specifications.

4. Fuel System Check

1. Connect a fuel pressure gauge to the fuel rail.
2. Turn the ignition key to the "ON" position without starting the engine and observe the fuel pressure reading.
3. If the pressure is low, check the fuel pump and filter for clogs or failures. Replace as necessary.

5. Inspect Vacuum Lines

1. Visually inspect all vacuum lines for cracks or disconnections.
2. Use a vacuum gauge to check for leaks if necessary.
3. Replace any damaged hoses or reconnect loose hoses.

6. Perform Compression Test

1. Remove the spark plugs and install the compression tester in the first cylinder.
2. Crank the engine for a few revolutions and record the pressure reading.
3. Repeat for all cylinders and compare results. If readings are low, further investigation is needed (such as checking for valve issues).