how to diagnose P0300 misfire code on Toyota Corolla E140 (2006-2013)

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, compression tester.
• Clear any existing codes from the ECU after diagnosis.
• Ensure the vehicle is parked on a level surface and the engine is cool.

2. Replace Spark Plugs

1. Disconnect the negative battery terminal.
2. Remove the ignition coil harness connectors.
3. Unscrew and remove the ignition coils using a socket.
4. Remove the old spark plugs using a spark plug socket.
5. Inspect the new spark plugs for the correct gap and install them, ensuring they are torqued to the manufacturer’s specifications (typically around 13-15 ft-lbs).
6. Reinstall the ignition coils and connect the harness connectors.

3. Inspect and Replace Ignition Coils (if necessary)

1. If any ignition coils were found faulty during diagnostics, remove them as per the previous step.
2. Install the new ignition coils, ensuring they are properly seated and connected.
3. Reconnect the negative battery terminal.

4. Check Fuel Injectors

1. Remove the fuel injector connectors.
2. Use a noid light to check for proper signal to the injectors when cranking the engine.
3. If injectors are faulty, remove the fuel rail and replace the injectors, ensuring they are properly seated and torqued.

5. Check for Vacuum Leaks

1. Inspect all vacuum lines and intake manifold gaskets visually and with a smoke test if necessary.
2. Replace any damaged vacuum hoses or gaskets.
3. Reassemble any components that were removed during inspection.