how to diagnose P0420 code on Honda Civic 10th Generation (2016-2021)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the negative battery terminal to prevent electrical shorts.
• Allow the engine to cool completely before starting work.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, torque wrench.
• Remove the upstream oxygen sensor first:
  • Disconnect the electrical connector.
  • Use the O2 sensor socket to unscrew the sensor.
• Install the new upstream oxygen sensor:
  • Apply anti-seize compound to the threads.
  • Torque to manufacturer specifications (usually around 30 lb-ft).
• Repeat the process for the downstream oxygen sensor if necessary.

3. Inspect and Replace Catalytic Converter

• Tools Required: Socket set, cutting tool (if necessary), exhaust sealant, jack stands.
• If the catalytic converter is damaged or blocked:
  • Remove any exhaust clamps or bolts securing the converter.
  • If it is welded in place, use a cutting tool to remove the old converter.
• Install the new catalytic converter:
  • Position the new converter and secure it with clamps or bolts.
  • Use exhaust sealant on joints to ensure a tight seal.
• Reconnect any oxygen sensors that were removed.

4. Reset the ECU

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code from the ECU.