how to fix P0420 code in BMW 5 Series G30/G31 (2017-2024)

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the battery to prevent any electrical shorts.
• Allow the vehicle to cool down before working on the exhaust system.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, socket set, torque wrench, penetrating oil
• Steps:
  1. Locate the upstream and downstream oxygen sensors (typically near the exhaust manifold and after the catalytic converter).
  2. Apply penetrating oil to the sensor threads if they are rusted or stuck.
  3. Disconnect the electrical connector from each O2 sensor.
  4. Using the O2 sensor socket, remove the old sensors.
  5. Install new oxygen sensors, tightening them to the manufacturer's specification (usually around 30 Nm).
  6. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter

• Tools Required: Jack and jack stands, socket set, exhaust pipe cutter, gaskets
• Steps:
  1. Raise the vehicle securely on jack stands and locate the catalytic converter.
  2. Inspect the catalytic converter for physical damage or clogs.
  3. If replacement is necessary, use an exhaust pipe cutter to remove the old catalytic converter.
  4. Clean the mounting surfaces of the exhaust pipes to ensure a good seal.
  5. Install the new catalytic converter along with new gaskets, securing it with bolts to the specified torque (usually around 40 Nm).
  6. Reconnect any heat shields or brackets that were removed during the process.

4. Reset the Engine Control Module (ECM)

• Tools Required: OBD-II scanner
• Steps:
  1. Once repairs are complete, reconnect the battery if it was disconnected.
  2. Use the OBD-II scanner to clear the P0420 code from the ECM.
  3. Start the engine and allow it to reach operating temperature.