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P0420 Honda Code - Catalyst System Efficiency Below Threshold Bank 1

- Code Popularity: 438,972 Views
- Repair Importance Level: 2/3
- Repair Difficulty Level: 2/3
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By AutoCodes.com - Updated Jul 03, 2020
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|Code P0420 Honda 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 the Code P0420 Honda?

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.

Does your Honda have Safety Recalls? → Check here

|Code P0420 Honda 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.

There is a Factory Service Bulletin for the following Honda models:
2003–2005 Honda Civic Hybrid ULEV (KA)
2002–2006 Honda Insight With M/T
Honda Civic, Insight Factory Service Bulletin OBDII Code P0420





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|What is the Cost to Diagnose the Code P0420 Honda?

Labor: 1.0

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

|When is the Code P0420 Honda Detected?

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

|What are Code P0420 Honda Possible Symptoms?

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

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

|Need More Information on the P0420 Honda Code?

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

|Need Help with the P0420 Honda Code?

Get the P0420 Honda code diagnosed by a professional: Find a repair shop in your area

|Code P0420 Honda comments

Help us improve AutoCodes.com. Leave a comment below or tell us if the information above helps you fix the code. What are the symptoms on your vehicle for the P0420 Honda code? Have you replaced any parts?
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