AutoCodes – Mitsubishi – P0420 Mitsubishi

P0420 Mitsubishi Code - Catalyst System Efficiency Below Threshold Bank 1

Quick Answer

The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor). Common causes include Faulty Three-way Catalyst Converter Bank 1, Exhaust Tube, Intake Air Leaks. 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 Three-way Catalyst Converter Bank 1, Exhaust Tube, Intake Air Leaks.
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.

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Code Popularity 79,915

How popular is this code, among other codes? Medium

Repair Importance Level

Moderate (Service soon) (2 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Aug 20, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0420 Mitsubishi Description

The Engine Control Module (ECM) monitors the switching frequency ratio of heated oxygen sensors 1 (front O2 sensor) and heated oxygen sensors 2 (rear O2 sensor).
A three way catalyst converter (Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.
When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst malfunction is diagnosed.

OBDII Code P0420 Mitsubishi - Catalyst System Efficiency Below Threshold Bank 1 - AutoCodes.com — P0420 Mitsubishi Code - Catalyst System Efficiency Below Threshold Bank 1

What does this mean?

What are the Possible Causes of the DTC P0420 Mitsubishi?

Faulty Three-way Catalyst Converter Bank 1
Exhaust Tube
Intake Air Leaks
Faulty Oxygen (O2) Sensor
Faulty Fuel injector(s)
Leaking Fuel Injector (s)
Faulty Spark plugs
Improper Ignition Timing
Faulty Engine Control Module (ECM)
Dirty Air Filter

How to Fix the DTC P0420 Mitsubishi?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

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.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0420 Mitsubishi code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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Need Help with the 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.