how to fix P0420 code on Honda Accord 8th Generation (2008-2012)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

1. Locate the oxygen sensors: Identify the upstream (pre-catalytic) and downstream (post-catalytic) sensors.
2. Remove the upstream oxygen sensor:
   • Use an oxygen sensor socket and ratchet to unscrew the sensor.
   • Disconnect the electrical connector.
3. Install the new upstream oxygen sensor:
   • Apply anti-seize compound to the threads of the new sensor.
   • Hand-tighten the sensor, then tighten to manufacturer specifications (typically around 30 Nm / 22 lb-ft).
4. Repeat for the downstream oxygen sensor if it is also faulty.

3. Inspect and Replace Catalytic Converter (if necessary)

1. Check the catalytic converter: If the converter shows signs of damage or blockage, proceed to replace it.
2. Remove the old catalytic converter:
   • Loosen and remove the bolts connecting the converter to the exhaust system.
   • Carefully detach the converter from the exhaust manifold and rear pipe.
3. Install the new catalytic converter:
   • Position the new converter and connect it to the exhaust manifold and rear pipe.
   • Use new gaskets and tighten the bolts to factory specifications (typically around 40 Nm / 30 lb-ft).

4. Reconnect Battery and Clear Codes

1. Reconnect the negative battery terminal securely.
2. Use an OBD-II scanner to clear the P0420 code from the vehicle's computer.