AutoCodes – Scion – P0420 Scion

P0420 Scion Code - Catalyst System Efficiency Below Threshold Bank 1

Quick Answer

The Engine Control Module (ECM) uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency. Common causes include Gas leak from exhaust system, Faulty Three-way Catalyst Converter Bank 1, Faulty Air Fuel Ratio (A/F) Sensor Bank 1 (Sensor 1 or Front Sensor or Upstream Sensor). 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 Scion indicates Catalyst System Efficiency Below Threshold Bank 1.
Common causes: Common causes include Gas leak from exhaust system, Faulty Three-way Catalyst Converter Bank 1, Faulty Air Fuel Ratio (A/F) Sensor Bank 1 (Sensor 1 or Front Sensor or Upstream Sensor).
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 38,183

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 Aug 27, 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 Scion Description

The Engine Control Module (ECM) uses sensors mounted in front of and behind the Three-Way Catalytic Converter (TWC) to monitor its efficiency.
The first sensor, the air-fuel ratio sensor, sends pre-catalyst information to the ECM. The second sensor, the heated oxygen sensor, sends post-catalyst information to the ECM.
In order to detect any deterioration in the three-way catalytic converter, the ECM calculates the oxygen storage capacity of the three-way catalytic converter. This calculation is based on the voltage output of the heated oxygen sensor while performing active air-fuel ratio control.
The oxygen storage capacity value is an indication of the oxygen storage capacity of the three-way catalytic converter. When the vehicle is being driven with a warm engine, active air-fuel ratio control is performed for approximately 15 to 20 seconds. When it is performed, the ECM deliberately sets the air-fuel ratio to lean or rich levels. If the cycle of the waveform for the heated oxygen sensor is long, the oxygen storage capacity is great. There is a direct correlation between the heated oxygen sensor and the oxygen storage capacity of the three-way catalytic converter.
The ECM uses the oxygen storage capacity value to determine the state of the three-way catalytic converter. If any deterioration has occurred, the ECM illuminates the MIL and stored the DTC.
This system determines the deterioration of the entire catalyst system (including the front and rear catalysts), by using the oxygen storage capacity value of the front catalyst, which is more sensitive than the rear catalyst, as the representative value. Therefore, be sure to replace the front and rear catalysts together when catalyst replacement is necessary.

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

What does this mean?

What are the Possible Causes of the DTC P0420 Scion?

Gas leak from exhaust system
Faulty Three-way Catalyst Converter Bank 1
Faulty Air Fuel Ratio (A/F) Sensor Bank 1 (Sensor 1 or Front Sensor or Upstream Sensor)
Faulty Heated Oxygen Sensor Bank 1 (Sensor 2 or Rear Sensor or Downstream Sensor)
Faulty Fuel Injector(s)

How to Fix the DTC P0420 Scion?

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 Engine Control Module (ECM) has detected that the Three-way Catalyst 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 Three-way Catalyst Converter 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 Scion 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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Information for Specific Scion Models

P0420 2005 Scion xB — Catalyst System Efficiency Below Threshold Bank 1
P0420 2006 Scion xB — Catalyst System Efficiency Below Threshold Bank 1
P0420 2007 Scion xB — Catalyst System Efficiency Below Threshold Bank 1

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 Scion Code

1. What are the common symptoms of an OBDII code P0420 in a Scion?

- Common symptoms include a check engine light, decreased fuel efficiency, rough idle, and potential loss of engine power.

2. What are the main causes of the P0420 code in a Scion?

- The main causes of the P0420 code are a faulty catalytic converter, oxygen sensor issues, exhaust leaks, or engine misfires.

3. How can I diagnose the P0420 code in my Scion?

- Diagnosing the P0420 code typically involves checking the oxygen sensor readings, inspecting the catalytic converter for damage, and examining the exhaust system for leaks.

4. Can I drive my Scion with a P0420 code?

- It is generally safe to drive your Scion with a P0420 code, but it is recommended to have the issue diagnosed and repaired as soon as possible to prevent potential damage to other components.

5. Are there any simple repair tips for fixing the P0420 code in my Scion?

- Simple repair tips include checking and replacing the oxygen sensors, repairing any exhaust leaks, and ensuring proper engine maintenance to prevent misfires.

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

- The cost of repairing a P0420 code in a Scion can vary depending on the specific cause, but it may range from $200 for minor repairs to over $1000 for a new catalytic converter.

7. Can I reset the P0420 code in my Scion by disconnecting the battery?

- While disconnecting the battery may temporarily clear the code, it is not a recommended long-term solution as the underlying issue causing the code will still need to be addressed.

8. Will using fuel additives help clear the P0420 code in my Scion?

- Fuel additives are unlikely to resolve the P0420 code as it is typically caused by mechanical issues with the catalytic converter or oxygen sensors that require proper repair.

9. How often should I have my Scion's catalytic converter inspected to prevent a P0420 code?

- It is recommended to have your Scion's catalytic converter inspected during regular maintenance intervals or if you notice any symptoms of a potential issue to prevent a P0420 code.

10. Can a P0420 code be triggered by a one-time issue in my Scion?

- While a one-time issue such as a sensor glitch or poor fuel quality may trigger a temporary P0420 code, it is important to have the issue diagnosed to prevent recurring problems.