how to fix P0420 code on Honda Civic 9th Generation (2012-2015)

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shock.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter
• Remove the upstream oxygen sensor using a socket wrench.
• Connect the multimeter to the sensor's terminals and check for proper voltage (should fluctuate between 0.1V and 0.9V).
• If the upstream sensor fails the test, replace it.

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

• Tools Required: Jack and jack stands, socket set, exhaust gasket
• Raise the vehicle and secure it with jack stands.
• Remove the bolts securing the catalytic converter to the exhaust manifold and the exhaust pipe. Use penetrating oil if necessary to loosen rusted bolts.
• Inspect the catalytic converter for physical damage or clogging. If damaged, replace it with a new unit.
• Install the new catalytic converter and tighten the bolts to the manufacturer's specifications (typically around 25-30 lb-ft).
• Replace any exhaust gaskets if necessary to prevent leaks.

4. Reinstall and Reconnect Components

• Reinstall the upstream oxygen sensor if it was removed.
• Reconnect the negative battery terminal.
• Clear the P0420 code using the OBD-II scanner.