how to fix a P0421 code on Volkswagen Golf Seventh Generation (2013-2020)?

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, socket set, torque wrench, backpressure gauge, safety glasses, gloves.
• Ensure the vehicle is parked on a flat surface and the engine is cool. Disconnect the battery's negative terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors on the exhaust system.
2. Remove the electrical connector from each oxygen sensor.
3. Using a socket wrench, carefully unscrew the sensors from their mounting locations.
4. Install new oxygen sensors (if faulty) and torque to manufacturer specifications.
5. Reconnect the electrical connectors securely.

3. Examine and Replace the Catalytic Converter (if necessary)

1. If the catalytic converter is found to be blocked or damaged, remove it by unbolting it from the exhaust system.
2. Install a new catalytic converter according to the manufacturer’s specifications, ensuring all gaskets are replaced.
3. Torque all exhaust bolts to the specified values to prevent exhaust leaks.

4. Reassemble and Reconnect

1. Reconnect the battery's negative terminal.
2. Start the engine and let it idle, checking for any exhaust leaks or abnormal noises.
3. Clear any trouble codes using the OBD-II scanner.