my Honda Civic 10th Generation (2016-2021) engine light is on with code P0420

Solution

1. Preparation

• Tools Required: OBD-II scanner, jack and jack stands, socket set, multimeter, safety glasses, gloves
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the negative battery terminal to prevent electrical shock.

2. Inspect and Replace Oxygen Sensors

• Sub-steps:
  1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors on the exhaust system.
  2. Using a socket wrench, remove the upstream oxygen sensor. (Torque specifications: 30-40 ft-lbs)
  3. Inspect the sensor for damage or contamination and replace if necessary.
  4. Repeat for the downstream oxygen sensor if it shows faulty readings.
  5. Connect the new sensors and secure them properly.

3. Inspect and Replace Catalytic Converter (if necessary)

• Sub-steps:
  1. Raise the vehicle using a jack and secure it with jack stands.
  2. Remove the bolts securing the catalytic converter to the exhaust pipe using a socket set.
  3. Carefully lower the catalytic converter from the vehicle.
  4. Inspect the old catalytic converter for damage or blockage; replace with a new unit if needed.
  5. Install the new catalytic converter and tighten the bolts to the manufacturer's specifications (typically 25-30 ft-lbs).

4. Reconnect Battery and Clear Codes

• Reconnect the negative battery terminal securely.
• Use the OBD-II scanner to clear the P0420 code from the vehicle’s computer.
• Ensure all connections are tight and secure before starting the engine.