AutoCodes - OBDII Code List - P0420
P0420 - Catalyst System Efficiency Below Threshold Bank 1
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P0420 Possible 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
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
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.User Submitted Video
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.
More Information
Need more information on how to fix the P0420 code?Get Access to Factory Service Manuals
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 MERCURY 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 ▶ 📷
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