what does it mean when my Honda Accord shows code P0420

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a flat surface and is securely elevated using jack stands if required.
• Disconnect the battery to prevent electrical shorts.

2. Inspect Oxygen Sensors

• Remove the upstream (pre-catalytic converter) oxygen sensor using a socket wrench.
• Inspect the sensor for damage or contamination.
• Use a multimeter to check the sensor resistance and ensure it is within specifications (refer to the vehicle service manual for specific values).
• If faulty, replace the oxygen sensor.

3. Inspect and Replace Catalytic Converter

• Remove the bolts securing the catalytic converter to the exhaust system, using a socket set.
• Carefully lower the catalytic converter from its position.
• Inspect for any physical damage or signs of clogging.
• If necessary, replace with a new catalytic converter, ensuring it meets OEM specifications.
• Reinstall the catalytic converter and torque the bolts to manufacturer specifications.

4. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear any stored trouble codes.
• Ensure that no other fault codes are present.