P0420 - Catalyst System Efficiency Below Threshold Bank 1

Repair Importance Level: 2/3
Repair Difficulty Level: 2/3

P0420 Causes

  • 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
  • P0420 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.





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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 labor rates vary widely across the country, and even within the same city. Most auto repairs shops charge between $75 and $150 per hour.

    P0420 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.

    P0420 Information for specific makes

  • P0420 ACURA Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 AUDI Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 BMW Catalytic Converter Conversion   
  • P0420 BUICK Catalyst System Low Efficiency Bank 1
  • P0420 CADILLAC Catalyst System Low Efficiency Bank 1
  • P0420 CHEVROLET Catalyst System Low Efficiency Bank 1
  • P0420 CHRYSLER Catalyst System Efficiency Bank 1   
  • P0420 DODGE Catalyst System Efficiency Bank 1   
  • P0420 FORD Catalyst System Efficiency Below Threshold Bank 1      
  • P0420 GMC Catalyst System Low Efficiency Bank 1
  • P0420 HONDA Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 HYUNDAI Warm Up Catalyst Efficiency Below Threshold Bank 1   
  • P0420 INFINITI Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 ISUZU Catalyst System Low Efficiency Bank 1   
  • P0420 JAGUAR Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 JEEP Catalyst System Efficiency Bank 1   
  • P0420 KIA Warm Up Catalyst Efficiency Below Threshold Bank 1   
  • P0420 LEXUS Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 MAZDA Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 MERCEDES-BENZ Catalyst System Efficiency Below Threshold Bank 1
  • P0420 MINI Catalytic Converter Conversion   
  • P0420 MITSUBISHI Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 NISSAN Catalyst System Efficiency Below Threshold Bank 1   
  • P0420 PONTIAC Catalyst System Low Efficiency Bank 1
  • P0420 SATURN Catalyst System Low Efficiency Bank 1
  • P0420 SCION Catalyst System Efficiency Below Threshold Bank 1
  • P0420 SUBARU Catalyst System Efficiency Below Threshold   
  • P0420 TOYOTA Catalyst System Efficiency Below Threshold Bank 1      
  • P0420 VOLKSWAGEN Catalyst System Efficiency Below Threshold Bank 1