my Ford Mustang S550 (2015-2023) has a check engine light with P0420 code

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Ensure the vehicle is parked on a flat surface and engage the parking brake.
• Disconnect the battery negative terminal to prevent electrical shorts.

2. Inspect and Replace the Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, multimeter.
• Remove the upstream oxygen sensor (located before the catalytic converter) using the O2 sensor socket.
• Install a new oxygen sensor and torque to manufacturer's specifications (typically around 30-40 lb-ft).
• Repeat the process for the downstream oxygen sensor (located after the catalytic converter).

3. Inspect and Replace the Catalytic Converter (if necessary)

• Tools Required: Socket set, exhaust pipe cutter, jack stands.
• Raise the vehicle and secure it with jack stands.
• Disconnect the exhaust system at the flanges before and after the catalytic converter.
• Remove any bolts or clamps securing the catalytic converter.
• Install the new catalytic converter and secure it with bolts at the flanges to the specified torque (usually around 30-40 lb-ft).
• Reconnect the exhaust system.

4. Reset the Engine Control Module (ECM)

• Reconnect the battery negative terminal.
• Use the OBD-II scanner to clear the check engine light and any stored codes.