my BMW 5 Series G30/G31 (2017-2024) has a check engine light with code P0420

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the vehicle's battery to ensure safety during repairs.
• Raise the vehicle using a jack and secure it with jack stands.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set
• Remove the upstream and downstream oxygen sensors from the exhaust system.
  • Sub-step: Disconnect the electrical connectors from each sensor.
  • Sub-step: Use the O2 sensor socket to unscrew the sensors from the exhaust pipes.
• Install new oxygen sensors.
  • Sub-step: Apply anti-seize compound to the threads of the new sensors.
  • Sub-step: Torque the new sensors to the manufacturer’s specifications (typically 30-40 Nm).
• Reconnect the electrical connectors to the new sensors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust hanger removal tool
• Remove the exhaust components to access the catalytic converter.
  • Sub-step: Unbolt the exhaust pipe from the catalytic converter.
  • Sub-step: Remove any exhaust hangers to free the converter.
• Inspect the catalytic converter for physical damage or blockage.
• If replacement is necessary, install the new catalytic converter.
  • Sub-step: Position the new catalytic converter in place.
  • Sub-step: Torque the bolts to the manufacturer’s specifications (refer to service manual for values).
• Reattach exhaust hangers and other components removed during disassembly.

4. Reconnect Battery and Clear Codes

• Reconnect the vehicle's battery.
• Use an OBD-II scanner to clear the P0420 code from the system.