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

Solution

1. Preparation

• Gather tools and parts: OBD-II scanner, socket set, multimeter, infrared thermometer, replacement oxygen sensors (if necessary).
• Ensure the vehicle is on a level surface, and the engine is off before starting work.

2. Inspect and Replace Oxygen Sensors

1. Disconnect Battery: Disconnect the negative terminal of the battery to prevent electrical shorts.
2. Remove Old Sensors:
   • Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
   • Use a socket or wrench to remove the sensors by turning them counterclockwise.
3. Install New Sensors:
   • Apply anti-seize compound to the threads of the new sensors.
   • Screw in the new sensors by hand and then tighten them with a wrench (do not overtighten).
4. Reconnect Battery: Reconnect the negative battery terminal.

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

1. Preparation: Raise the vehicle securely on jack stands and ensure it is cool.
2. Remove Exhaust Components:
   • Use a socket set to remove the bolts securing the exhaust pipe to the catalytic converter.
   • Disconnect any hangers or brackets holding the exhaust system in place.
3. Inspect Catalytic Converter:
   • Visually inspect for external damage or signs of blockage.
   • If damaged, proceed to replace it.
4. Install New Catalytic Converter:
   • Position the new catalytic converter and secure it with the original or new bolts.
   • Reattach the exhaust pipe and any hangers or brackets removed earlier.
5. Check for Leaks: Start the engine and inspect for exhaust leaks in the system.