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

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 Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Inspect the wiring and connectors of both the upstream and downstream oxygen sensors for damage or corrosion.
• Use a multimeter to check the voltage output of the upstream oxygen sensor. It should fluctuate between 0.1V to 0.9V.
• If the readings are out of range, replace the faulty oxygen sensor.

3. Inspect Catalytic Converter

• Tools Required: Jack and jack stands, exhaust pipe cutter
• Raise the vehicle using a jack and secure it with jack stands.
• Visually inspect the catalytic converter for physical damage or signs of clogging.
• If the converter appears damaged or has a restricted flow, it needs to be replaced.

4. Replace Catalytic Converter

• Tools Required: Socket set, torque wrench, exhaust sealant
• Remove the exhaust pipes connected to the catalytic converter using a socket set.
• Detach the catalytic converter from the exhaust manifold carefully.
• Install the new catalytic converter and tighten the bolts to the manufacturer’s specified torque settings.
• Apply exhaust sealant to ensure a proper seal.

5. Reconnect Battery and Reset ECU

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the ECU.
• Start the engine and allow it to reach operating temperature.