how to fix P0421 code in Tesla Model S Plaid/Refresh (2021-present)

Learn how to diagnose and fix P0421 exhaust system issue in Tesla Model S Plaid. Step-by-step guide with diagnostic procedures and repair instructions.

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 to prevent electrical shorts.

2. Inspect Oxygen Sensors

• Tools Required: O2 sensor socket, multimeter
• Remove the upstream and downstream oxygen sensors.
• Use a multimeter to test the voltage output of the sensors. The upstream sensor should fluctuate between 0.1V and 0.9V; the downstream sensor should be relatively stable.
• Replace any malfunctioning sensors.

3. Examine the Catalytic Converter

• Tools Required: Jack and jack stands, socket set
• Lift the vehicle securely using a jack and jack stands.
• Inspect the catalytic converter for physical damage or signs of blockage (e.g., excessive soot or rattling).
• If damaged, remove the catalytic converter using a socket set and replace it with a new unit.

4. Repair Exhaust Leaks

• Tools Required: Exhaust pipe cutter, welding equipment or exhaust clamp
• Check the exhaust system for any leaks, especially near the catalytic converter.
• Use an exhaust pipe cutter to cut out damaged sections, then weld or clamp new exhaust components in place as needed.

5. Reassemble and Reset

• Reinstall all components, including the oxygen sensors and any affected exhaust parts.
• Reconnect the negative battery terminal.
• Use an OBD-II scanner to clear the trouble codes and reset the check engine light.