AutoCodes – Mercedes-Benz – P0420 Mercedes-Benz

P0420 Mercedes-Benz 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 Mercedes-Benz 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 60,209

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 Mercedes-Benz 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 Mercedes-Benz - Catalyst System Efficiency Below Threshold Bank 1 - AutoCodes.com — P0420 Mercedes-Benz Code - Catalyst System Efficiency Below Threshold Bank 1

What does this mean?

What are the Possible Causes of the DTC P0420 Mercedes-Benz?

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 Mercedes-Benz?

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 Mercedes-Benz 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.

Need more information about the P0420 Mercedes-Benz code?

Need more information on how to fix the P0420 Mercedes-Benz code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P0420 Mercedes-Benz code diagnosed by a professional: Find a repair shop in your area

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 Mercedes-Benz Code

1. What are common symptoms of an OBDII code P0420 in a Mercedes-Benz?

- Common symptoms include decreased fuel efficiency, engine misfires, and the illumination of the check engine light.

2. What are the possible causes of the P0420 code in a Mercedes-Benz?

- The P0420 code in a Mercedes-Benz may be caused by a faulty catalytic converter, oxygen sensor issues, exhaust leaks, or engine misfires.

3. How can I diagnose the cause of the P0420 code in my Mercedes-Benz?

- Diagnosing the P0420 code may involve inspecting the catalytic converter, checking the oxygen sensor readings, conducting a visual inspection for exhaust leaks, and performing engine diagnostics.

4. Can I continue driving my Mercedes-Benz with a P0420 code?

- It is not recommended to continue driving your Mercedes-Benz with a P0420 code, as it can lead to further damage to the engine and emissions system.

5. How much does it typically cost to repair a P0420 code in a Mercedes-Benz?

- The cost of repairing a P0420 code in a Mercedes-Benz can vary depending on the underlying cause, but it may range from a few hundred to a few thousand dollars.

6. Are there any DIY tips for repairing a P0420 code in a Mercedes-Benz?

- DIY tips for repairing a P0420 code may include checking for loose connections, replacing the oxygen sensor yourself, or using fuel additives to clean the catalytic converter.

7. Can a P0420 code be triggered by a one-time issue in a Mercedes-Benz?

- A P0420 code in a Mercedes-Benz may sometimes be triggered by a temporary issue, but it is important to diagnose and address the root cause to prevent further problems.

8. Will resetting the check engine light make the P0420 code go away in a Mercedes-Benz?

- Resetting the check engine light may temporarily clear the P0420 code, but if the underlying issue is not addressed, the code is likely to reappear.

9. How long does it take to repair a P0420 code in a Mercedes-Benz?

- The repair time for a P0420 code in a Mercedes-Benz can vary depending on the specific cause and complexity of the issue, but it may take a few hours to a day.

10. Can a P0420 code affect the performance of a Mercedes-Benz?

- Yes, a P0420 code can affect the performance of a Mercedes-Benz by causing decreased fuel efficiency, reduced engine power, and potential drivability issues.