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AutoCodes - Honda - P0420 HONDA

P0420 HONDA Code - Catalyst System Efficiency Below Threshold Bank 1

- Code Popularity: 426,983 Views
- Repair Importance Level: 2/3
- Repair Difficulty Level: 2/3
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By - Updated Jul 03, 2020
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|P0420 HONDA code 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 HONDA code?

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.

|P0420 HONDA code 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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|Cost of diagnosing P0420 HONDA code

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 P0420 HONDA 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.

|What are P0420 HONDA code possible symptoms?

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

|P0420 HONDA code 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 -
P0420 HONDA Code - Catalyst System Efficiency Below Threshold Bank 1

|Need more information with the P0420 HONDA code?

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|Need help with a P0420 HONDA code?

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|P0420 HONDA code comments

Help us improve 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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