how to fix P0421 code in Honda Accord 10th Generation (2018-2022)

Learn how to diagnose and fix P0421 warm up catalyst efficiency issue in Honda Accord 10th Generation. Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

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

Tools Required:

• OBD-II scanner
• Multimeter
• Infrared thermometer
• Socket set
• Torque wrench

2. Inspect and Test Oxygen Sensors

• Sub-steps:
  1. Locate the upstream and downstream oxygen sensors.
  2. Disconnect the electrical connectors from both sensors.
  3. Use a multimeter to check the voltage of the upstream sensor; it should fluctuate between 0.1 to 0.9 volts.
  4. If the readings are out of range, replace the faulty oxygen sensor.

3. Inspect and Test Catalytic Converter

• Sub-steps:
  1. Check for any physical damage or blockage in the catalytic converter.
  2. Use an infrared thermometer to measure the temperature at the inlet and outlet of the catalytic converter.
  3. The outlet temperature should be significantly higher than the inlet (ideally around 100°F hotter).
  4. If temperatures do not meet specifications, replace the catalytic converter.

4. Clear Codes and Test Drive

• Sub-steps:
  1. Reconnect the battery terminal.
  2. Use the OBD-II scanner to clear the P0421 code from the ECU.
  3. Start the engine and allow it to reach operating temperature.
  4. Take the vehicle for a test drive to ensure the code does not reappear.