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.
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
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.
- Three way catalytic converter Bank 1 does not operate properly.
- Three way catalyst converter Bank 1 does not have enough oxygen storage capacity.
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.
Need more information on how to fix the P0420 HONDA code?
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