AutoCodes - OBDII Code List - P0420

P0420 - Catalyst System Efficiency Below Threshold Bank 1

Repair Importance Level: 2/3
Repair Difficulty Level: 2/3
What does this mean?
Table of contents

P0420 Possible Causes

What does this mean?
  • 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 do I fix code P0420?

Check the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.
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Tech Notes

What does this mean?
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.





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Cost of diagnosing the P0420 code

Labor: 1.0

The cost of diagnosing the P0420 code is 1.0 hour of labor. The auto repair's diagnosis time and labor rates vary by location, vehicle's make and model, and even your engine type. Most auto repair shops charge between $75 and $150 per hour.

When is the code detected?

- Three way catalytic converter Bank 1 does not operate properly.
- Three way catalyst converter Bank 1 does not have enough oxygen storage capacity.

Possible Symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)

P0420 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 - Catalyst System Efficiency Below Threshold Bank 1 - AutoCodes.com

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