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P0420 Mitsubishi Code - Catalyst System Efficiency Below Threshold Bank 1

Quick Answer

The P0420 diagnostic trouble code (DTC) for Mitsubishi vehicles indicates that the catalyst system's efficiency is below the threshold on bank 1. Common causes include Faulty catalytic converter, Oxygen sensor malfunction, Exhaust leaks or damage. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

What it means
P0420 Mitsubishi indicates Catalyst System Efficiency Below Threshold Bank 1.
Common causes
Common causes include Faulty catalytic converter, Oxygen sensor malfunction, Exhaust leaks or damage.
Severity
Moderate - service should be scheduled soon.
Can I drive?
The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.
What is this?
Table of contents Created and updated by William Orellana on Aug 30, 2024
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Code P0420 Mitsubishi Description

The P0420 diagnostic trouble code (DTC) for Mitsubishi vehicles indicates that the catalyst system's efficiency is below the threshold on bank 1. This means that the catalytic converter is not performing its job effectively in reducing harmful emissions from the exhaust gases. The catalytic converter is a crucial component in the emission control system, converting harmful pollutants such as carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful emissions like carbon dioxide and water vapor.

OBDII Code P0420 Mitsubishi - Catalyst System Efficiency Below Threshold Bank 1
P0420 Mitsubishi Code - Catalyst System Efficiency Below Threshold Bank 1

Common Causes of P0420 Mitsubishi

  1. Faulty catalytic converter
  2. Oxygen sensor malfunction
  3. Exhaust leaks or damage
  4. Engine misfires
  5. Rich fuel mixture

Symptoms of P0420 Mitsubishi

  1. Check Engine Light illuminated on the dashboard
  2. Decreased fuel efficiency
  3. Reduced engine performance or power
  4. Rattling or unusual noises coming from the exhaust system
  5. Failed emissions test

How to Fix P0420 Mitsubishi

  1. Diagnose the issue by using a scan tool to confirm the P0420 code and inspecting the catalytic converter, oxygen sensors, and exhaust system for any damage or malfunction.
  2. Replace the catalytic converter if it is determined to be faulty and not functioning properly.
  3. Replace any malfunctioning oxygen sensors or repair exhaust leaks to ensure proper air-fuel mixture and exhaust gas flow.
  4. Address any engine misfires or fuel system issues that could be contributing to the problem.
  5. Clear the trouble code and perform a test drive to ensure the issue has been resolved.

Cost to Fix P0420 Mitsubishi

The cost of repairing a P0420 diagnostic code can vary depending on the specific cause of the issue. On average, replacing a catalytic converter can range from $500 to $2000, including parts and labor. Oxygen sensor replacement can cost around $200 to $300 per sensor, and addressing exhaust leaks or other issues may incur additional costs. It is recommended to consult with a qualified mechanic or auto repair shop for a more accurate estimate based on your vehicle's make and model. Keep in mind that labor rates can vary, so it's advisable to inquire about rates in your local area.

What does this mean?

Tech Notes for P0420 Mitsubishi

As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.

When is the Code Detected?

- Three way catalytic converter Bank 1 does not operate properly.
- Three way catalyst converter Bank 1 does not have enough oxygen storage capacity.

Need more information about the P0420 Mitsubishi code?

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0420 Mitsubishi Code

1. What are the common symptoms of an OBDII code P0420 in a Mitsubishi?

The common symptoms include decreased fuel efficiency, rough idling, loss of engine power, and the illumination of the Check Engine light.

2. What are the possible causes of a P0420 code in a Mitsubishi?

Possible causes include a faulty catalytic converter, oxygen sensor issues, exhaust system leaks, engine misfires, or issues with the fuel system.

3. How serious is an OBDII code P0420 in a Mitsubishi?

While the car may still be operational with this code, it is important to address it promptly as it can lead to increased emissions, decreased performance, and potential damage to other components over time.

4. Can I continue driving my Mitsubishi with a P0420 code?

It is generally safe to drive the vehicle for a short period after the code appears, but it is recommended to have it diagnosed and repaired by a qualified mechanic as soon as possible.

5. How can I diagnose the cause of a P0420 code in my Mitsubishi?

Diagnosing the issue typically involves conducting a thorough inspection of the catalytic converter, oxygen sensors, exhaust system, and engine components using diagnostic tools and equipment.

6. What are some repair tips for fixing a P0420 code in a Mitsubishi?

Repair tips may include replacing the catalytic converter, oxygen sensors, spark plugs, or addressing any exhaust leaks present in the system.

7. Can I reset the OBDII code P0420 in my Mitsubishi without fixing the underlying issue?

While you can clear the code using an OBDII scanner, it will likely return if the root cause is not addressed. It is best to fix the underlying problem to prevent further issues.

8. How much does it cost to repair a P0420 code in a Mitsubishi?

The cost of repairs can vary widely depending on the specific issue causing the code, the model of the Mitsubishi, and labor costs. It is advisable to obtain quotes from different mechanics for an accurate estimate.

9. Will a P0420 code cause my Mitsubishi to fail emissions testing?

Yes, a P0420 code indicates that the catalytic converter is not functioning efficiently, which can lead to increased emissions. This may cause the vehicle to fail emissions testing in some regions.

10. Can a DIY enthusiast fix a P0420 code in a Mitsubishi?

While some aspects of diagnosing and repairing the issue may be within the capabilities of a skilled DIY enthusiast, it is recommended to consult a professional mechanic for proper diagnosis and repair to ensure the problem is fully resolved.

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