how to fix P0420 code on Honda Accord 9th Generation (2013-2017)

Honda Accord Eleventh Generation (2023-present)

Error Codes

2-4 hours

Time

medium

Difficulty

high

Severity

Error Code: P0420

3 min read

551 words

⚠️ Safety Warning

This issue requires immediate attention. If you are not experienced with automotive repairs, consult a professional mechanic. Working on critical systems can be dangerous.

Problem Statement

Learn how to diagnose and fix P0420 code on Honda Accord 9th Generation. Step-by-step guide with symptoms, diagnostic steps, and repair instructions.

Error Code

P0420

Affected Component

Exhaust System

Estimated Time

2-4 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical systems.
•Allow the exhaust system to cool before touching any components.

Symptoms

•Check engine light illuminated
•Poor fuel economy
•Decreased engine performance
•Sulfur smell from exhaust
•Failed emissions test

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0420 and check for additional codes.
2
Inspect the exhaust system for any visible leaks or damage.
3
Test the oxygen sensors (upstream and downstream) for proper functioning using a multimeter.
4
Check the fuel trim readings to assess if the engine is running rich or lean.
5
Perform a visual inspection of the catalytic converter for physical damage or signs of clogging.
6
Use a vacuum gauge to check for exhaust restrictions.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•OBD-II scanner
•Multimeter
•Socket set
•Jack and jack stands
•Safety goggles
•Gloves

Parts Required

•Oxygen sensors (upstream and downstream)
•Catalytic converter (if damaged)

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Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0420 and check for additional codes.
2
Inspect the exhaust system for any visible leaks or damage.
3
Test the oxygen sensors (upstream and downstream) for proper functioning using a multimeter.
4
Check the fuel trim readings to assess if the engine is running rich or lean.
5
Perform a visual inspection of the catalytic converter for physical damage or signs of clogging.
6
Use a vacuum gauge to check for exhaust restrictions.

Solution

1. Preparation

Tools Required: OBD-II scanner, multimeter, socket set, jack and jack stands, safety goggles, and gloves.
Allow the vehicle to cool down completely before starting work.
Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Oxygen Sensors (if faulty)

Sub-steps:
1. Locate the upstream (pre-catalytic) and downstream (post-catalytic) oxygen sensors.
2. Disconnect the electrical connectors from both sensors.
3. Use a socket wrench to remove the sensors from the exhaust manifold and catalytic converter.
4. Install new oxygen sensors by reversing the removal process, ensuring they are torqued to manufacturer's specifications (typically 30 lb-ft).
5. Reconnect the electrical connectors to the sensors.

3. Inspect and Replace Catalytic Converter (if necessary)

Sub-steps:
1. Remove the exhaust pipes connected to the catalytic converter using a socket set.
2. Inspect the catalytic converter for internal damage or excessive clogging.
3. If replacement is required, install the new catalytic converter, ensuring proper alignment and sealing.
4. Torque the connection bolts to manufacturer's specifications (generally around 40-50 lb-ft).
5. Reattach any exhaust hangers and pipes that were removed.

4. Clear Codes and Test

Sub-steps:
1. Reconnect the negative battery terminal.
2. Use an OBD-II scanner to clear the P0420 code from the vehicle's computer.
3. Start the vehicle and allow it to reach operating temperature.
4. Take the vehicle for a test drive to ensure the check engine light does not reappear.