how to diagnose a P0420 code on my Honda Accord 9th Generation (2013-2017)

Solution

1. Preparation

• Gather tools and parts needed for repair.
• Disconnect the negative battery terminal for safety.

2. Inspect and Test Oxygen Sensors

• Tools Required: OBD-II scanner, multimeter, socket set.
• Remove the upstream and downstream oxygen sensors.
• Use a multimeter to measure the voltage output of the upstream sensor; it should fluctuate between 0.1 to 0.9 volts.
• Check the downstream sensor; it should have a steady voltage (around 0.5 volts) under normal operating conditions.
• If either sensor is faulty, replace it.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, jack and jack stands, exhaust pipe cutter (if necessary).
• Raise the vehicle safely using jack stands.
• Inspect the catalytic converter for physical damage or clogging.
• If damage is found, remove the exhaust pipes connected to the catalytic converter using a socket set.
• Remove the catalytic converter and replace it with a new unit, ensuring proper alignment and fit.
• Reattach the exhaust pipes and ensure all connections are secure.

4. Clear Codes and Test Drive

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the ECM.
• Perform a test drive to monitor for any reoccurrence of the code.