my Volkswagen Golf MK7 (2015-2019) has a check engine light and code P0304

Solution

1. Preparation

• Tools Required: Socket set, torque wrench, spark plug socket, compression tester.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery cable to prevent electrical shorts.

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

• Remove the engine cover if applicable.
• Use a socket wrench to remove the bolt securing the ignition coil for cylinder 4.
• Pull the ignition coil out of the spark plug hole.
• Remove the spark plug using a spark plug socket and ratchet.
• Inspect the spark plug for wear or carbon buildup.
• Install a new spark plug (torque to manufacturer specifications, typically around 22 lb-ft).
• Insert the new ignition coil into the spark plug hole and secure it with the bolt.

3. Inspect and Test Fuel Injector

• Disconnect the electrical connector from the fuel injector for cylinder 4.
• Use a multimeter to check the injector's resistance (specifications typically around 12-16 ohms).
• If the injector is faulty, replace it with a new one and reconnect the electrical connector.

4. Perform Compression Test

• Remove the spark plugs from all cylinders.
• Insert the compression tester into the cylinder 4 spark plug hole.
• Crank the engine for a few seconds and record the compression reading.
• Compare with manufacturer specifications (typically 150-200 psi).
• Repeat for other cylinders to ensure consistency.

5. Check for Vacuum Leaks

• Inspect all vacuum lines connected to the intake manifold for cracks or disconnections.
• Use a smoke machine or carb cleaner to detect vacuum leaks while the engine is running.
• Repair or replace any faulty vacuum lines or intake gaskets as necessary.