how to fix P0420 code on my Ford Mustang S550 (2015-2023)?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle battery to ensure safety.
• Raise the vehicle securely on jack stands.

2. Inspect and Replace Oxygen Sensors

1. Remove the upstream oxygen sensor:
   • Locate the upstream oxygen sensor (usually before the catalytic converter).
   • Use an oxygen sensor socket to carefully unscrew and remove the sensor.
2. Install the new oxygen sensor:
   • Apply anti-seize compound to the threads of the new sensor (if applicable).
   • Screw in the new sensor by hand to avoid cross-threading, then tighten securely with the socket (typically 30 Nm).
3. Repeat for the downstream oxygen sensor if it’s also suspected to be faulty.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Remove the catalytic converter:
   • Unbolt the exhaust flanges connecting the catalytic converter to the exhaust pipes.
   • Use a socket set and wrench to remove any heat shields or brackets.
   • Carefully extract the catalytic converter from the vehicle.
2. Install the new catalytic converter:
   • Position the new catalytic converter into the exhaust system.
   • Reattach flanges and any heat shields or brackets, ensuring connections are tight (follow manufacturer torque specifications).
3. Reconnect any sensors if removed during the process.

4. Reconnect Battery and Clear Codes

• Reconnect the vehicle battery terminals.
• Use the OBD-II scanner to clear the trouble codes from the ECU.