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

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, multimeter, exhaust leak detection tool.
• Disconnect the negative battery terminal to ensure safety while working on the vehicle.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors on the exhaust system.
2. Remove the electrical connectors from both sensors.
3. Use a socket wrench to carefully unscrew the sensors from the exhaust pipes.
4. Install the new oxygen sensors by screwing them into place and reconnecting the electrical connectors.
   • Torque Specification: Tighten to manufacturer specifications (usually around 30 Nm).

3. Inspect and Replace Catalytic Converter

1. If the oxygen sensors are functioning correctly, inspect the catalytic converter for blockage.
   • Use a vacuum gauge to check if back pressure is within normal limits (usually 1-2 psi at idle).
2. If the catalytic converter is clogged or damaged, remove it from the exhaust system.
   • Use a socket set to unbolt the catalytic converter from the exhaust pipes.
3. Install the new catalytic converter by reversing the removal steps.
   • Torque Specification: Tighten bolts to manufacturer specifications.

4. Clear Codes and Test Drive

1. Reconnect the negative battery terminal.
2. Use an OBD-II scanner to clear the P0420 code from the ECU.
3. Test drive the vehicle for at least 20 miles to verify that the issue has been resolved and the check engine light does not reappear.