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)
When is the code detected?
- 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.
P0420 Honda Information for specific Honda models
P0420 1997 HONDA CIVIC
P0420 1998 HONDA CIVIC
P0420 1999 HONDA CIVIC
P0420 2000 HONDA CIVIC