why is my Honda Civic 9th Generation (2012-2015) check engine light on with code P0420

Solution

1. Preparation

• Gather tools and parts needed for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Locate the upstream and downstream oxygen sensors.
2. Disconnect the wiring harness from each sensor.
3. Use an O2 sensor socket to remove the sensors from the exhaust system.
4. Install new oxygen sensors:
   • Apply anti-seize compound to the threads of the new sensors.
   • Torque to manufacturer specifications (typically around 30 lb-ft).
5. Reconnect the wiring harness to each sensor.

3. Examine and Replace the Catalytic Converter

1. Remove the exhaust pipe sections connected to the catalytic converter:
   • Use a socket set to remove any bolts or nuts securing the exhaust.
   • Support the exhaust system to prevent damage.
2. Inspect the catalytic converter for damage; if it is clogged or damaged, proceed to replace it.
3. Install the new catalytic converter:
   • Ensure the gasket is in place, then connect the exhaust pipe sections.
   • Torque the bolts to manufacturer specifications.
4. Reconnect any heat shields or brackets that were removed.

4. Reset the Engine Control Module (ECM)

1. Reconnect the negative battery terminal.
2. Use an OBD-II scanner to clear the P0420 code from the ECM.
3. Start the vehicle and allow it to reach operating temperature.