P0420 HONDA - Catalyst System Efficiency Below Threshold Bank 1
- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM)
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.
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.
- Engine Light ON (or Service Engine Soon Warning Light)
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.
HONDA Technical Service Bulletins for P0420 code
2007 HONDA FIT Engine And Engine Cooling:engine Details
2007 HONDA FIT Power Train:automatic Transmission:control Module (tcm, Pcm) Details
2008 HONDA FIT Engine And Engine Cooling:engine Details
2008 HONDA FIT Power Train:automatic Transmission:control Module (tcm, Pcm) Details
2003 HONDA CIVIC Electrical System Details
2004 HONDA CIVIC Electrical System Details
2005 HONDA CIVIC Electrical System Details
1996 HONDA CIVIC Engine And Engine Cooling:engine Details
1997 HONDA CIVIC Engine And Engine Cooling:engine Details
1998 HONDA CIVIC Engine And Engine Cooling:engine Details
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