how to resolve P0420 code on my Volkswagen Passat B8 (2015-2022)

Solution

1. Preparation

• Gather tools and parts needed.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream oxygen sensor (before the catalytic converter) using the O2 sensor socket.
• Inspect the sensor for damage or contamination; replace if necessary.
• Repeat for the downstream oxygen sensor (after the catalytic converter).
• Torque the new sensors to the manufacturer's specification (usually around 30 lb-ft).

3. Inspect and Replace Catalytic Converter (if needed)

• Tools Required: Socket set, jack and jack stands, WD-40 or penetrating oil.
• Raise the vehicle securely with jack stands.
• Spray the bolts connecting the catalytic converter to the exhaust system with penetrating oil and allow it to soak.
• Remove the bolts and disconnect the catalytic converter from the exhaust system.
• Inspect for clogs or physical damage; if damaged, replace with a new catalytic converter.
• Install the new catalytic converter and torque the bolts to the manufacturer’s specifications.

4. Engine Management Reset

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the vehicle's computer.
• Start the engine and allow it to reach operating temperature.