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

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors (if faulty)

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the upstream oxygen sensor:
  1. Locate the upstream oxygen sensor, usually before the catalytic converter.
  2. Use the O2 sensor socket to unscrew the sensor.
  3. Install the new sensor and torque it to the manufacturer's specification (typically around 30 Nm).
• Repeat for the downstream oxygen sensor if it also tested faulty.

3. Inspect Catalytic Converter

• Tools Required: Visual inspection tools, flashlight
• Check for signs of physical damage or clogging:
  1. Inspect the exterior of the catalytic converter for dents, rust, or leaks.
  2. Tap gently on the converter with your hand; listen for rattling sounds which indicate internal failure.
• If damaged, proceed to replace the catalytic converter.

4. Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust sealant, new gaskets
• Remove the old catalytic converter:
  1. Disconnect any exhaust clamps and bolts securing the converter.
  2. Remove the old converter from the exhaust system.
• Install the new catalytic converter:
  1. Position the new converter in place with new gaskets.
  2. Secure it with bolts and clamps, torquing to manufacturer's specifications (typically 30-50 Nm).

5. Reset the OBD-II System

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to erase the P0420 code and any other stored codes.