how to fix P0420 Honda Accord 9th Generation (2013-2017) emissions issue

Solution

1. Preparation

• Gather all necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the parking brake is engaged.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Tools Required: Oxygen sensor socket, wrench set, multimeter.
• Remove the upstream (pre-catalytic converter) oxygen sensor:
  1. Locate the sensor on the exhaust manifold.
  2. Use the oxygen sensor socket to unscrew the sensor.
  3. Install the new oxygen sensor and tighten to manufacturer specifications (typically around 30 lb-ft).
• Repeat for the downstream (post-catalytic converter) oxygen sensor if it shows signs of failure.

3. Inspect the Catalytic Converter

• Tools Required: Jack stands, torque wrench.
• To check for a faulty catalytic converter:
  1. Visually inspect for physical damage or signs of overheating (discoloration).
  2. Use a temperature gun to measure the inlet and outlet temperatures. The outlet should be significantly hotter (at least 100°F higher) than the inlet.
  3. If it’s defective, remove the catalytic converter by loosening the exhaust clamps and bolts connecting it to the exhaust system.
  4. Install a new catalytic converter and secure it, tightening the bolts to the manufacturer's torque specifications.

4. Clear the Codes

• Reconnect the negative battery terminal.
• Use the OBD-II scanner to clear the P0420 code.
• Start the vehicle and allow it to reach operating temperature.