how to fix P0421 code in Renault Clio V (2019-Present)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Disconnect the battery to prevent electrical shorts.
• Allow the engine to cool down if it has been running.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, torque wrench, multimeter
• Locate the upstream (pre-catalytic) oxygen sensor and the downstream (post-catalytic) oxygen sensor.
• Disconnect the electrical connectors from both oxygen sensors.
• Use the O2 sensor socket to remove the sensors from their respective locations.
• Inspect the threads and connectors for damage; replace if necessary.
• Install new oxygen sensors by screwing them in hand-tight, then torque to the manufacturer’s specifications (usually around 30 ft-lbs).
• Reconnect the electrical connectors.

3. Inspect and Replace Catalytic Converter (if necessary)

• Tools Required: Socket set, torque wrench, exhaust gasket
• Inspect the catalytic converter for any physical damage or clogging.
• If replacement is necessary, remove the exhaust bolts securing the catalytic converter using a socket set.
• Replace the old catalytic converter with a new one, ensuring proper alignment.
• Torque the bolts to the manufacturer’s specified torque settings.
• Replace any exhaust gaskets that may be worn or damaged.

4. Clear Codes and Test

• Reconnect the battery.
• Use an OBD-II scanner to clear the trouble codes from the vehicle's computer.
• Test drive the vehicle to ensure that the check engine light does not reappear.