how to diagnose a P0301 misfire code in my Toyota Highlander Fourth Generation (2020-present)?

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.

2. Inspect and Replace Spark Plug

1. Remove the engine cover if necessary.
2. Disconnect the ignition coil harness for cylinder 1.
3. Remove the ignition coil using a socket wrench.
4. Remove the spark plug using a spark plug socket.
5. Inspect the spark plug for wear and replace it if damaged or fouled.
6. Install the new spark plug with the correct gap (usually 0.043 inches for most Toyota engines).
7. Reinstall the ignition coil and reconnect the harness.

3. Test and Replace Ignition Coil

1. If the spark plug is fine, test the ignition coil using a multimeter for proper resistance.
2. If the resistance is out of spec, replace the ignition coil with a new one.
3. Reinstall the ignition coil and reconnect the harness.

4. Inspect Fuel Injector

1. Disconnect the fuel injector connector for cylinder 1.
2. Use a multimeter to check for proper voltage and continuity to the injector.
3. If the injector is faulty, replace it with a new one.
4. Reconnect the fuel injector connector.

5. Perform Compression Test

1. Remove the spark plug for cylinder 1 and insert the compression tester.
2. Crank the engine and observe the pressure reading.
3. If the compression is low, further diagnosis is required to determine internal engine issues.

6. Check for Vacuum Leaks

1. Inspect vacuum hoses and gaskets around the intake manifold for any visible damage.
2. Use a smoke machine or carb cleaner to check for leaks while the engine is idling.
3. Repair any leaks found.