how to fix P0421 code in Honda Accord 9th Generation (2013-2017)

Learn how to diagnose and fix P0421 exhaust system issue in Honda Accord (2013-2017). Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the engine is cool.
• Disconnect the battery to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors

• Step 1: Remove the upstream oxygen sensor using an O2 sensor socket.

• Step 2: Inspect the sensor for damage or excessive carbon buildup. Replace if necessary.

• Step 3: Install a new oxygen sensor, tighten to manufacturer specifications (typically 30-40 lb-ft).

• Step 4: Repeat the process for the downstream oxygen sensor if it appears faulty.

3. Inspect and Replace Catalytic Converter (if necessary)

• Step 1: If the catalytic converter is suspected to be faulty, unbolt the exhaust pipes connected to it using a socket set.

• Step 2: Remove any heat shields or brackets securing the catalytic converter.

• Step 3: Inspect the catalytic converter for signs of clogging or physical damage. Replace it if necessary.

• Step 4: Install the new catalytic converter in reverse order, ensuring all bolts are tightened to manufacturer specifications (usually around 25-30 lb-ft).

4. Reconnect Battery and Clear Codes

• Step 1: Reconnect the negative battery terminal.
• Step 2: Use the OBD-II scanner to clear the P0421 code from the vehicle’s computer.