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

Solution

1. Preparation

• Gather necessary tools and parts.
• Park the vehicle on a level surface and ensure the engine is cool.
• Disconnect the negative battery terminal to avoid electrical shorts.

2. Replace Faulty Oxygen Sensors

• Tools Required: O2 sensor socket, ratchet, torque wrench
• Remove the pre-catalytic (upstream) oxygen sensor by:
  1. Locating the sensor on the exhaust manifold.
  2. Using the O2 sensor socket to unscrew the sensor.
  3. Installing the new sensor and tightening it to the manufacturer’s specifications (usually around 30 lb-ft).
• Repeat for the post-catalytic (downstream) oxygen sensor.

3. Inspect and Replace Catalytic Converter

• Tools Required: Jack and jack stands, socket set, torque wrench
• Raise the vehicle using a jack and secure it with jack stands.
• Remove the exhaust system components connected to the catalytic converter:
  1. Unbolt the flange connections and remove any hangers.
  2. Take out the old catalytic converter.
• Install the new catalytic converter:
  1. Position the new converter in place.
  2. Bolt it securely, ensuring not to overtighten (typically 25 lb-ft).
  3. Reattach the exhaust system components in reverse order.

4. Clear Codes and Test Drive

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Test drive the vehicle for 10-15 minutes to monitor if the check engine light returns.