how to fix P0420 catalyst efficiency below threshold in Honda Civic 10th Generation (2016-2021)

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery by removing the negative terminal to prevent any electrical issues.
• Raise the vehicle using a jack and secure it with jack stands.

2. Inspect and Replace Oxygen Sensors

• Tools Required: O2 sensor socket, wrench set, torque wrench.

• Remove the pre-catalytic oxygen sensor first:

  1. Locate the sensor on the exhaust manifold.
  2. Disconnect the wiring harness from the sensor.
  3. Using the O2 sensor socket, unscrew the sensor.
  4. Install the new sensor by screwing it into place and tightening it to manufacturer specifications (approximately 30 lb-ft).

• Repeat the process for the post-catalytic oxygen sensor if necessary.

3. Inspect or Replace the Catalytic Converter

• Tools Required: Socket set, exhaust pipe cutter, gasket scraper.

• Inspect the catalytic converter for damage:

  1. Check for any visible dents, rust, or holes.
  2. If damaged, cut the exhaust pipe before and after the catalytic converter using an exhaust pipe cutter.
  3. Remove the old catalytic converter.

• Install the new catalytic converter:

  1. Clean the exhaust pipe ends with a gasket scraper.
  2. Position the new catalytic converter and secure it with the appropriate bolts and gaskets.
  3. Tighten the bolts to specified torque (usually around 30-40 lb-ft, check manufacturer specs).

4. Reset the Engine Control Module (ECM)

• After repairs, reconnect the battery.
• Use the OBD-II scanner to clear the P0420 code from the system.
• Start the engine and allow it to run for a few minutes.