how to diagnose the P0301 misfire code on 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.
• Disconnect the negative battery terminal to prevent any electrical shorts.

2. Inspect and Replace Spark Plug

• Remove the engine cover if applicable.
• Locate the spark plug for cylinder 1 (typically the first plug on the engine).
• Use a spark plug socket and ratchet to remove the spark plug.
• Inspect the spark plug for signs of wear (burnt, cracked, or fouled).
• If damaged, replace with a new spark plug, ensuring it meets manufacturer specifications for gap and heat range.

3. Check and Replace Ignition Coil

• Disconnect the electrical connector from the ignition coil located on cylinder 1.
• Remove the mounting bolts securing the ignition coil using a socket set.
• Inspect the ignition coil for cracks or signs of overheating.
• If faulty, replace the ignition coil with a new unit, ensuring it is securely fastened and the connector is properly attached.

4. Perform Compression Test

• Remove the spark plug from cylinder 1 and insert a compression gauge into the spark plug hole.
• Crank the engine a few times to get a compression reading.
• Compare the reading to the manufacturer’s specifications. If low, further investigation into the engine's internal components may be necessary.

5. Inspect Fuel Injector

• Disconnect the fuel injector connector for cylinder 1.
• Use a multimeter to check the injector's resistance; it should typically be within the range specified by the manufacturer.
• If the injector is faulty, replace it, ensuring to use a new O-ring and reconnect the electrical connector.