my Volkswagen Golf MK7 (2015-2019) has a P0421 code, what's the solution?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle's battery to prevent electrical issues.
• Ensure the car is parked on a level surface and secure it with wheel chocks.

Tools Required:

• OBD-II scanner
• Multimeter
• Infrared thermometer
• Socket set
• Torque wrench
• Jack and jack stands

2. Inspect and Test O2 Sensors

1. Locate the upstream and downstream oxygen sensors in the exhaust system.
2. Disconnect the wiring harness from both sensors.
3. Use a multimeter to check the resistance of the sensors; replace any that are out of specification.
4. If the pre-catalytic sensor is functioning correctly, proceed to the next step.

3. Replace Catalytic Converter (if necessary)

1. If tests indicate a faulty catalytic converter, prepare to replace it.
2. Remove the exhaust heat shield if applicable (usually held by bolts).
3. Use a socket set to remove the bolts securing the catalytic converter to the exhaust system.
4. Carefully detach the catalytic converter, ensuring not to damage surrounding components.
5. Install the new catalytic converter, ensuring proper alignment.
6. Torque the mounting bolts to the manufacturer’s specifications (refer to the service manual for exact torque values).

4. Reconnect and Test

1. Reconnect the oxygen sensor wiring harnesses.
2. Reconnect the vehicle’s battery.
3. Start the engine and let it warm up to operating temperature.