how to diagnose a P0301 code in my Toyota Highlander Third Generation (2014-2019)

Solution

1. Preparation

• Gather tools and parts required.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal for safety.

2. Replace Spark Plug and Ignition Coil (if faulty)

• Tools Required: Socket set, torque wrench, dielectric grease.
• Remove the engine cover (if applicable).
• Disconnect the electrical connector from the ignition coil of cylinder 1.
• Remove the ignition coil by unscrewing it using the socket set.
• Remove the spark plug using the socket.
• Inspect the spark plug for wear, carbon buildup, or damage.
• Install a new spark plug, ensuring it is gapped correctly (usually between 0.043" to 0.046").
• Apply dielectric grease to the ignition coil boot before reinstalling.
• Reinstall the ignition coil and reconnect the electrical connector.

3. Inspect and Replace Fuel Injector (if necessary)

• Tools Required: Fuel injector removal tool, fuel line disconnect tool.
• Relieve fuel pressure by removing the fuel pump fuse and starting the engine until it stalls.
• Disconnect the electrical connector and fuel line from the fuel injector.
• Remove the fuel injector from the rail, taking care not to damage the O-rings.
• Inspect the injector for clogs or damage; replace if necessary.
• Install the new fuel injector and reconnect the fuel line and electrical connector.

4. Perform Compression Test

• Tools Required: Compression gauge.
• Remove the spark plug from cylinder 1.
• Screw the compression gauge into the spark plug hole.
• Crank the engine a few times to get a reading and compare with manufacturer specifications.
• If the compression is low, further engine diagnostics may be necessary.