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

Solution

1. Preparation

• Gather tools: OBD-II scanner, spark plug socket, compression tester, multimeter, and basic hand tools.
• Ensure the vehicle is parked on a level surface and the engine is cool.

2. Inspect and Replace Spark Plug

• Remove the engine cover if necessary.
• Disconnect the ignition coil connector and remove the ignition coil.
• Use a spark plug socket to remove the spark plug from cylinder 1.
• Inspect the spark plug for damage; replace it if worn or fouled.
• Install a new spark plug, ensuring it is gapped correctly, and torque it to the manufacturer’s specifications (typically around 13-15 lb-ft).
• Reinstall the ignition coil and reconnect the connector.

3. Test and Replace Ignition Coil

• If the spark plug is fine, use a multimeter to check the resistance of the ignition coil.
• If outside manufacturer specifications, replace the ignition coil with a new one.
• Reinstall the ignition coil and reconnect the electrical connector.

4. Perform Compression Test

• Remove the spark plug from cylinder 1 and install the compression tester.
• Crank the engine a few times and take the reading.
• Compare the reading to the manufacturer’s specifications; if low, it may indicate internal engine issues.

5. Inspect Fuel Injector

• Check the fuel injector for cylinder 1 using a noid light to ensure it’s receiving a signal.
• If there’s no signal, check wiring and connectors for damage.
• If the injector is faulty, replace it with a new one.

6. Check for Vacuum Leaks

• Inspect all hoses connected to the intake manifold for cracks or disconnections.
• Use a smoke machine or carburetor cleaner to check for vacuum leaks around the intake manifold and throttle body.
• Repair or replace any damaged components.