AutoCodes – GMC – P0420 2017 GMC Sierra

P0420 2017 GMC Sierra Code - Catalyst System Low Efficiency Bank 1

Quick Answer

A 3-way catalyst controls emissions of hydrocarbons, Carbon Monoxide (CO), and Nitrogen Oxide (NOx). 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 2017 GMC Sierra indicates Catalyst System Low Efficiency 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 385

How popular is this code, among other codes? Low

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 Jun 20, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0420 2017 GMC Sierra Description

A 3-way catalyst controls emissions of hydrocarbons, Carbon Monoxide (CO), and Nitrogen Oxide (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbons and the CO that are present in the exhaust gas. This process converts the hydrocarbons and the CO into water vapor and carbon dioxide (CO2), and reduces the NOx, converting the NOx into nitrogen. The catalyst also stores oxygen. The Engine Control Module (ECM) monitors this process by using Heated Oxygen Sensors (HO2S) that are in the exhaust stream before and after the 3- way catalyst. The HO2S produces an output signal that the ECM uses to calculate the oxygen storage capacity of the catalyst. This indicates the ability of the catalyst to convert the exhaust emissions efficiently. The ECM monitors the efficiency of the catalyst by monitoring the HO2S during an off-idle, Decel Fuel Cut-Off (DFCO) event. When the catalyst is functioning properly, the post-catalyst HO2S response to the fuel conditions during the DFCO event is slow compared to the response of the pre-catalyst HO2S. When the post-HO2S response is near that of the pre-HO2S, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold. The Diagnostic Trouble Code (DTC) will be set when the ECM determines that the efficiency of the catalyst has degraded below a calibrated threshold.

OBDII Code P0420 2017 GMC Sierra - Catalyst System Low Efficiency Bank 1 - AutoCodes.com — P0420 2017 GMC Sierra Code - Catalyst System Low Efficiency Bank 1

What does this mean?

What are the Possible Causes of the DTC P0420 2017 GMC Sierra?

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 2017 GMC Sierra?

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 (it 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 2017 GMC Sierra 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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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 2017 GMC Sierra Code

1. What are the common symptoms of OBDII code P0420 in a 2017 GMC Sierra?

The common symptoms of P0420 include a check engine light, decreased fuel efficiency, and potential lack of power or performance issues.

2. What does the "Catalyst System Low Efficiency Bank 1" mean in relation to OBDII code P0420?

This code indicates that the catalytic converter in Bank 1 of the exhaust system is not functioning efficiently to reduce emissions.

3. What are the possible causes of OBDII code P0420 in a 2017 GMC Sierra?

Common causes of P0420 include a faulty catalytic converter, oxygen sensor issues, exhaust leaks, or engine misfires.

4. Can a bad oxygen sensor trigger code P0420 in a 2017 GMC Sierra?

Yes, a malfunctioning oxygen sensor can send incorrect data to the engine control module, leading to a diagnosis of low catalyst efficiency and triggering code P0420.

5. How can I diagnose the root cause of OBDII code P0420 in my 2017 GMC Sierra?

A proper diagnosis involves checking the catalytic converter, oxygen sensors, exhaust system for leaks, and ensuring there are no engine misfires.

6. Is it safe to continue driving with OBDII code P0420 in a 2017 GMC Sierra?

While the vehicle may still be operable with this code, it is recommended to address the issue promptly to prevent potential damage to other components and ensure compliance with emission regulations.

7. Can a catalytic converter cleaner fix OBDII code P0420 in a 2017 GMC Sierra?

Catalytic converter cleaners may help in some cases by removing carbon buildup, but they are not a guaranteed solution for a failing catalytic converter triggering P0420.

8. Do I need to replace the catalytic converter if OBDII code P0420 appears in my 2017 GMC Sierra?

If other potential causes have been ruled out and the catalytic converter is indeed faulty, replacement may be necessary to resolve the P0420 code and restore proper emissions control.

9. How much does it typically cost to repair OBDII code P0420 in a 2017 GMC Sierra?

The cost of repairing P0420 can vary depending on the root cause, but it may involve replacing oxygen sensors, fixing exhaust leaks, or replacing the catalytic converter, with total costs ranging from a few hundred to over a thousand dollars.

10. Can resetting the OBDII code P0420 in a 2017 GMC Sierra temporarily resolve the issue?

Resetting the code may temporarily turn off the check engine light, but it will not fix the underlying problem causing P0420. It is recommended to diagnose and address the root cause for a lasting solution.