how to fix P0421 code in Volkswagen Golf Seventh Generation (2013-2020)

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Safety gear: gloves and safety glasses.
• Disconnect the battery to avoid electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Locate the Oxygen Sensors:

   • The upstream sensor is typically located before the catalytic converter, and the downstream sensor is after it.

2. Remove Oxygen Sensors:

   • Use a socket wrench to unscrew the sensors.
   • Be cautious not to damage the wiring harness.

3. Install New Oxygen Sensors:

   • Apply anti-seize compound to the threads of the new sensors.
   • Hand-tighten the sensors then use the socket wrench to secure them to the specified torque (usually around 30-40 Nm).

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove Exhaust Components:

   • Disconnect exhaust hangers and remove bolts securing the catalytic converter to the exhaust manifold and exhaust pipe.

2. Inspect the Catalytic Converter:

   • Look for physical damage or excessive carbon buildup.

3. Install New Catalytic Converter:

   • Position the new converter and secure it with bolts to the exhaust manifold and exhaust pipe.
   • Tighten all bolts to manufacturer specifications (typically around 40-50 Nm).

4. Reset the ECU

• Reconnect the battery and use an OBD-II scanner to clear the P0421 code from the ECU.
• Start the engine and allow it to reach operating temperature.