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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to ensure safety.

2. Inspect and Replace Oxygen Sensors

1. Locate the Oxygen Sensors:
   • Identify the pre-catalytic (upstream) and post-catalytic (downstream) oxygen sensors.
2. Remove the Sensors:
   • Use a socket wrench with an oxygen sensor socket to unscrew and remove each sensor.
3. Install New Sensors:
   • Apply anti-seize compound to the threads of the new sensors.
   • Screw in the new sensors and tighten to the manufacturer’s specifications (typically 30 Nm).

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove Exhaust Components:
   • Loosen and remove any clamps and bolts securing the exhaust system to access the catalytic converter.
2. Remove the Catalytic Converter:
   • Disconnect the converter from the exhaust manifold and the exhaust pipe.
3. Install New Catalytic Converter:
   • Position the new converter in place and secure it using original hardware or new gaskets and bolts as required.
   • Torque the bolts to the specified torque value (typically 40-50 Nm).

4. Reconnect Battery and Clear Codes

1. Reconnect Battery:
   • Reconnect the negative terminal of the battery.
2. Clear the Error Codes:
   • Use an OBD-II scanner to clear the P0420 code and any other stored codes.