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

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to prevent any electrical shorts.
• Allow the vehicle to cool down before working on the exhaust system.

2. Inspect and Replace Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter, socket set, oxygen sensor socket.
• Check the voltage output of the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
  • If the upstream sensor is not switching between 0.1V and 0.9V, replace it.
  • If the downstream sensor does not show a stable voltage (typically around 0.5V after warm-up), replace it as well.
• To replace the sensors:
  1. Use an oxygen sensor socket to unscrew the faulty sensor from the exhaust manifold or catalytic converter.
  2. Install the new sensor and torque it to the manufacturer's specifications (usually around 30-40 ft-lbs).
  3. Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust hanger removal tool.
• If oxygen sensors are functioning properly and the P0420 code persists:
  1. Remove exhaust hangers and brackets holding the catalytic converter in place.
  2. Disconnect the exhaust pipes from the catalytic converter using a socket set.
  3. Remove the old catalytic converter.
  4. Install the new catalytic converter, ensuring it is properly aligned.
  5. Reconnect the exhaust pipes and secure with appropriate torque.
  6. Reattach hangers and brackets.