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

4 min read

653 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 exhaust system issue in Honda Accord 9th Generation (2013-2017). Step-by-step guide with diagnostic procedures 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 negative battery terminal to prevent electrical shorts.
•Allow the engine to cool before working on the exhaust system.

Symptoms

•Check engine light illuminated
•Decreased fuel efficiency
•Rough engine performance or misfires
•Failed emissions test
•Unusual exhaust smells (e.g., sulfur or rotten egg odor)
•Increased engine temperatures

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0420 and check for any additional codes.
2
Inspect the exhaust system for visible leaks or damage, particularly around the catalytic converter.
3
Measure the voltage output of the upstream and downstream O2 sensors using a multimeter to assess their function.
4
Check the catalytic converter's temperature using an infrared thermometer; the inlet temperature should be lower than the outlet temperature if the converter is functioning correctly.
5
Inspect the vehicle’s fuel trim values with the scanner to rule out fuel delivery issues that could affect catalytic converter efficiency.
6
Verify that there are no exhaust restrictions, including a blocked muffler or exhaust pipe.

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
•Infrared thermometer
•Socket set
•Torque wrench
•Safety goggles

Parts Required

•Upstream O2 sensor
•Downstream O2 sensor
•Catalytic converter (if necessary)

Related Faults

Share this solution

Comments

No comments yet

Be the first to share your thoughts

Back to Generation

Diagnostic Steps

1
Scan for error codes using an OBD-II scanner to confirm P0420 and check for any additional codes.
2
Inspect the exhaust system for visible leaks or damage, particularly around the catalytic converter.
3
Measure the voltage output of the upstream and downstream O2 sensors using a multimeter to assess their function.
4
Check the catalytic converter's temperature using an infrared thermometer; the inlet temperature should be lower than the outlet temperature if the converter is functioning correctly.
5
Inspect the vehicle’s fuel trim values with the scanner to rule out fuel delivery issues that could affect catalytic converter efficiency.
6
Verify that there are no exhaust restrictions, including a blocked muffler or exhaust pipe.

Solution

1. Preparation

Gather tools: OBD-II scanner, multimeter, infrared thermometer, socket set, torque wrench, and safety goggles.
Disconnect the negative battery terminal to prevent electrical shorts.
Allow the engine to cool before working on the exhaust system.

2. Replace Faulty O2 Sensors

Locate the O2 Sensors: Identify the upstream and downstream O2 sensors. The upstream sensor is located before the catalytic converter, and the downstream sensor is after it.
Remove the Old O2 Sensors:
- Use a socket or wrench to unscrew the O2 sensors.
- Carefully disconnect the electrical connectors.
Install New O2 Sensors:
- Apply anti-seize compound to the threads of the new O2 sensors.
- Install the upstream sensor first, followed by the downstream sensor.
- Connect the electrical connectors to both sensors.
- Torque the sensors to the manufacturer’s specifications (typically around 30 lb-ft).

3. Inspect and Replace Catalytic Converter (if necessary)

Assess Catalytic Converter Condition: If O2 sensor replacement does not resolve the issue, inspect the catalytic converter for internal damage or blockage.
Remove the Old Catalytic Converter:
- Disconnect the exhaust pipes at the flanges using appropriate tools.
- Remove any heat shields or mounting brackets.
- Unbolt the catalytic converter from the exhaust system.
Install New Catalytic Converter:
- Position the new catalytic converter in place.
- Bolt it securely to the exhaust system, ensuring proper alignment.
- Reattach any heat shields or brackets.
- Torque bolts to manufacturer specifications.

4. Clear Codes and Test Drive

Reconnect Battery: Reconnect the negative battery terminal.
Clear the P0420 Code: Use the OBD-II scanner to erase the trouble codes.
Test Drive: Drive the vehicle for at least 20-30 minutes to allow the ECU to perform self-tests and check for the reappearance of the P0420 code.