my Ford Mustang S550 (2015-2023) check engine light is on with code P0420, how to fix?

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, torque wrench, backpressure gauge, safety glasses, gloves, jack stands.
• Allow the engine to cool down before beginning any work. Disconnect the battery to ensure safety.

2. Check and Replace Oxygen Sensors

• Step 1: Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
• Step 2: Disconnect the electrical connectors from both oxygen sensors.
• Step 3: Use a socket to remove the sensors from their respective locations.
• Step 4: Install new oxygen sensors, ensuring to tighten them to the manufacturer’s specified torque (usually around 30 ft-lbs).
• Step 5: Reconnect the electrical connectors to the new sensors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Step 1: Raise the vehicle securely using jack stands.
• Step 2: Inspect the catalytic converter for physical damage or blockage.
• Step 3: If replacement is needed, remove the bolts securing the catalytic converter to the exhaust system using a socket set.
• Step 4: Carefully detach the catalytic converter from the exhaust system.
• Step 5: Install the new catalytic converter, aligning it properly with the exhaust pipes.
• Step 6: Tighten all bolts to the manufacturer’s specified torque (usually around 40 ft-lbs).

4. Reset Check Engine Light

• Step 1: Reconnect the battery.
• Step 2: Use an OBD-II scanner to clear the check engine light.
• Step 3: Start the engine and allow it to reach operating temperature.