how to fix P0420 code on Ford Mustang S650 (2024-Present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the vehicle's battery to prevent electrical shorts.
• Allow the engine to cool before starting work on the exhaust system.

2. Inspect Oxygen Sensors

• Sub-steps:
  • Locate the upstream and downstream oxygen sensors.
  • Disconnect the electrical connectors.
  • Use a multimeter to test the resistance of each sensor: the upstream sensor should show variable voltage between 0.1V to 0.9V while the engine is running; the downstream should be fairly stable.
  • Replace any faulty sensors.

3. Inspect and Clean the Catalytic Converter

• Sub-steps:
  • Remove the catalytic converter from the exhaust system using a socket set.
  • Inspect the converter for any physical damage or clogging.
  • If cleanable, use a catalytic converter cleaner and follow the manufacturer’s instructions.
  • If heavily damaged or clogged, replace the catalytic converter with a new, OEM-specified unit.

4. Reassemble and Test

• Sub-steps:
  • Reinstall the catalytic converter and ensure all bolts are tightened to the manufacturer's torque specifications (typically 25-30 lb-ft).
  • Reconnect the oxygen sensors and battery.
  • Start the engine and allow it to reach operating temperature.

5. Clear Codes

• Sub-steps:
  • Use the OBD-II scanner to clear the P0420 code from the ECU.
  • Perform a test drive to confirm that the check engine light does not reappear.