how to fix P0421 code in BMW X5 F15 (2014-2019)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal.

2. Inspect and Replace Oxygen Sensors

• Tools Required: Socket set, O2 sensor wrench.
• Remove the upstream oxygen sensor (pre-catalytic converter) by unscrewing it from the exhaust manifold.
• Inspect the sensor for damage or contamination; replace if necessary.
• Install the new oxygen sensor, ensuring it is secured to the specified torque (usually around 30 Nm).
• Repeat for the downstream sensor (post-catalytic converter) if needed.

3. Inspect and Replace Catalytic Converter (if required)

• Tools Required: Jack and jack stands, socket set, exhaust pipe cutter (if needed).
• Raise the vehicle safely using jack stands.
• Inspect the catalytic converter for any signs of physical damage or blockage.
• If replacement is necessary, unbolt the catalytic converter from the exhaust system and remove it.
• Install the new catalytic converter, making sure to use new gaskets and secure bolts to the specified torque (typically around 30-40 Nm).

4. Clear Error Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0421 code from the vehicle's computer.

5. Test Drive

• Start the engine and allow it to reach operating temperature.
• Take the vehicle for a test drive to ensure the check engine light does not return and performance is restored.