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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative terminal of the battery to prevent electrical shorts.
• Allow the engine to cool down before starting work.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench.
• Remove the upstream and downstream oxygen sensors:
  1. Locate the oxygen sensors on the exhaust manifold and downstream of the catalytic converter.
  2. Use the O2 sensor socket to carefully unscrew each sensor.
• Install new oxygen sensors:
  1. Apply anti-seize compound to the threads of the new sensors.
  2. Hand-tighten the sensors, then torque them to the manufacturer’s specifications (usually around 30 Nm).

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, jack stands, exhaust pipe cutter (if needed).
• Remove the catalytic converter:
  1. Raise the vehicle securely on jack stands.
  2. Disconnect any clamps or bolts securing the catalytic converter to the exhaust system.
  3. If necessary, cut the exhaust pipes carefully using an exhaust pipe cutter.
• Install the new catalytic converter:
  1. Position the new catalytic converter and secure it with the original or new clamps/bolts.
  2. Ensure all connections are tight and sealed properly.

4. Clear Codes and Test Drive

• Tools Required: OBD-II scanner.
• Clear the P0420 code from the vehicle's computer using the scanner.
• Test drive the vehicle for at least 15-20 minutes to verify the repair and monitor engine performance.