how to fix P0420 code on BMW 3 Series E90/E91 (2005-2012)

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, socket set, torque wrench, and possibly a replacement catalytic converter or oxygen sensors.
• Ensure the vehicle is parked on a level surface and set the parking brake.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Disconnect the negative battery terminal to prevent electrical shorts.
  2. Locate the pre-catalytic and post-catalytic oxygen sensors on the exhaust system.
  3. Use a socket wrench to remove the sensors.
  4. Inspect the connectors for damage or corrosion; clean if necessary.
  5. Install new oxygen sensors, tightening to manufacturer specifications (usually around 30 Nm).
  6. Reconnect the battery terminal.

3. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. Raise the vehicle using jack stands and ensure safety.
  2. Remove the exhaust heat shield if applicable.
  3. Unbolt the catalytic converter from the exhaust system using a socket set.
  4. Inspect the old catalytic converter for any signs of blockage or damage.
  5. Install the new catalytic converter, ensuring proper alignment and sealing.
  6. Torque all bolts to manufacturer specifications (typically around 40 Nm).
  7. Reinstall the exhaust heat shield.