AutoCodes – BMW – P0420 BMW

P0420 BMW Code - Catalytic Converter Conversion

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 BMW indicates Catalytic Converter Conversion.
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.

Save to My Repairs Step-by-Step Diagnostic Guide My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 80,843

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
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

Code P0420 BMW 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 BMW - Catalytic Converter Conversion - AutoCodes.com — P0420 BMW Code - Catalytic Converter Conversion

What does this mean?

What are the Possible Causes of the DTC P0420 BMW?

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 BMW?

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 BMW 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 BMW code?

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

Need Help with the Code?

Get the P0420 BMW 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 BMW Code

1. What are common symptoms of a P0420 code in a BMW?

- Common symptoms include a check engine light, decreased fuel efficiency, and a lack of engine power.

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

- Possible causes include a faulty catalytic converter, oxygen sensor issues, exhaust leaks, or engine misfires.

3. Can a P0420 code be caused by a bad oxygen sensor in a BMW?

- Yes, a failing oxygen sensor can lead to a P0420 code as it affects the readings that determine the efficiency of the catalytic converter.

4. How can I diagnose the root cause of a P0420 code in my BMW?

- Diagnosing the issue may require checking the oxygen sensor readings, inspecting the catalytic converter for damage, and examining the exhaust system for leaks.

5. Can I drive my BMW with a P0420 code?

- It is not recommended to drive with a P0420 code for an extended period as it may lead to further damage to the catalytic converter and reduce engine performance.

6. How much does it typically cost to repair a P0420 code in a BMW?

- The cost of repair can vary depending on the underlying issue, but it may range from a few hundred to over a thousand dollars for parts and labor.

7. Are there any DIY tips for resolving a P0420 code in a BMW?

- DIY tips may include checking and replacing oxygen sensors, inspecting for exhaust leaks, and ensuring proper engine maintenance to address potential causes.

8. Is it necessary to replace the catalytic converter when dealing with a P0420 code in a BMW?

- In some cases, replacing the catalytic converter may be necessary to resolve a P0420 code, especially if it is confirmed to be faulty or damaged.

9. How long does it take to repair a P0420 code in a BMW?

- The repair time can vary based on the specific issue, but it may take a few hours to a full day for a professional mechanic to diagnose and fix the problem.

10. Can a P0420 code reappear after it has been cleared in a BMW?

- Yes, a P0420 code can reappear if the underlying issue has not been fully resolved, so it is essential to address all potential causes during the repair process.