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

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the vehicle to cool down if the engine has been running.

2. Inspect and Replace Oxygen Sensors

1. Locate the Oxygen Sensors:

   • Identify the upstream (pre-catalytic) and downstream (post-catalytic) O2 sensors.
   • Tools Required: O2 sensor socket or wrench.

2. Test Oxygen Sensors:

   • Use a multimeter to measure the voltage output of both sensors. The upstream sensor should fluctuate between 0.1 to 0.9 volts, while the downstream sensor should show a more stable voltage.

3. Replace Faulty Sensors:

   • If either sensor is faulty, unscrew the sensor using the O2 sensor socket.
   • Apply anti-seize compound to the threads of the new sensor and install it.
   • Torque the sensor to manufacturer specifications (generally around 30 lb-ft).

3. Inspect and Replace Catalytic Converter (if necessary)

1. Visual Inspection:

   • Examine the catalytic converter for any signs of physical damage or rattling.

2. Check for Exhaust Leaks:

   • Use a smoke machine or listen for leaks around the catalytic converter and exhaust joints.

3. Remove and Replace the Catalytic Converter:

   • If damaged, unbolt the catalytic converter from the exhaust system. Tools Required: Socket set, torque wrench.
   • Install the new catalytic converter and ensure all bolts are torqued to the specified settings (usually around 40 lb-ft).
   • Reconnect any oxygen sensors if they were removed during the process.