AutoCodes – Saturn – P0420 Saturn

P0420 Saturn 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 Saturn 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.

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 61,519

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 Jun 20, 2022

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 Saturn 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 Saturn - Catalyst System Low Efficiency Bank 1 - AutoCodes.com — P0420 Saturn Code - Catalyst System Low Efficiency Bank 1

What does this mean?

What are the Possible Causes of the DTC P0420 Saturn?

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 Saturn?

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 Saturn 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 Saturn code?

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

Need Help with the Code?

Get the P0420 Saturn 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 Saturn Code

1. What are the common symptoms of OBDII code P0420 on a Saturn, indicating Catalyst System Low Efficiency Bank 1?

- Typical symptoms include reduced fuel efficiency, a noticeable decrease in engine performance, and the illumination of the Check Engine Light.

2. What are the possible causes of OBDII code P0420 on a Saturn?

- Common causes include a faulty catalytic converter, oxygen sensor issues (particularly the downstream sensor), exhaust leaks, or engine misfires.

3. How can I diagnose the root cause of OBDII code P0420 on my Saturn?

- Diagnosing this code usually involves checking the catalytic converter's efficiency, inspecting the oxygen sensors, examining the exhaust system for leaks, and verifying proper engine operation.

4. Can a bad oxygen sensor trigger OBDII code P0420 on a Saturn?

- Yes, a malfunctioning downstream oxygen sensor can send inaccurate data to the engine control module, leading to the triggering of code P0420.

5. What are some repair tips for addressing OBDII code P0420 on a Saturn?

- Repair options may include replacing the catalytic converter, repairing any exhaust leaks, replacing faulty oxygen sensors, fixing engine misfires, and resetting the Check Engine Light.

6. Is it safe to continue driving my Saturn with OBDII code P0420 present?

- While the vehicle may still be operable with this code, driving with a malfunctioning catalytic converter can potentially lead to increased emissions and further damage to the engine components.

7. Can I reset the Check Engine Light to see if OBDII code P0420 on my Saturn returns?

- Resetting the Check Engine Light may temporarily clear the code, but it's important to address the underlying issue causing code P0420 to prevent future problems.

8. How much does it typically cost to repair OBDII code P0420 on a Saturn?

- The cost of repairs for code P0420 can vary depending on the specific issue, but it may range from a few hundred dollars for oxygen sensor replacement to over a thousand dollars for catalytic converter replacement.

9. Are there any recalls or technical service bulletins related to OBDII code P0420 on Saturn vehicles?

- It's recommended to check with the manufacturer or a Saturn dealership to inquire about any recalls or technical service bulletins related to code P0420 for your specific vehicle model and year.

10. Can a DIY enthusiast address OBDII code P0420 on a Saturn, or is professional help necessary?

- While some basic troubleshooting and repairs can be done by DIYers, diagnosing and repairing complex issues causing code P0420 may require professional tools and expertise, especially when dealing with the catalytic converter.

Discuss the causes and fixes for P0420 Saturn OBDII Code

Submit a New Comment

Cheston Moore
Date: March 15, 2014 at 1:55 pm

For my Saturn SL2, the PCM threw the P0420 code, but the problem was a restricted muffler. The inside of the muffler had rusted out and pieces were blocking the tailpipe. This caused gases to back up to the rear O2 sensor and show an inefficient catcon.
So, check for muffler restriction prior to replacing a $130+ converter.

Reply to Comment
Margreen
Date: December 28, 2014 at 2:24 pm

My engine began missing about 2 months ago, in a bad rainstorm. Then it dried out and was OK, for a few days. Now, it misses every opportunity it gets, and I have replaced the MAP sensor and spark plugs plus boots, per a dealer's recommendation (but I only spent about $60 for parts, and did not pay them the $400+ they wanted). One friend who helped with the plugs gave me a bottle of Techron fuel system cleaner, too, and that's in the tank now, but I still have the problem. It was also suggested it could be a faulty gas cap, but replacing that did not help. It absolutely gulps gas when it's missing, and I dare not drive it far.
My nephew used to work at a dealership with a Saturn mechanic. He suggested (after I had tried 3 other fixes) that I replace the coolant temperature sensor. On to AutoZone, again.

Reply to Comment
OBDIITech
Date: December 28, 2014 at 7:08 pm

Thanks for the information. I hope the sensor fix the problem.

Reply to Comment
Margreen
Date: December 28, 2014 at 7:53 pm

As soon as some mechanically-oriented friend with the proper socket wrench volunteers to help change it, we'll see. This morning, on the way to AutoZone, the light was on, but at least it didn't miss. I don't know if leaving the car out in the cold overnight helped, or the new gas cap helped, or ...?

Reply to Comment