P0420 SUBARU - Catalyst System Efficiency Below Threshold
- 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
Tech notesAs 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 Subaru DescriptionThe 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 help?Get the P0420 Subaru code diagnosed by a professional: Find a repair shop in your area
P0420 SUBARU CommentsHelp us improve AutoCodes.com. Leave a comment below or tell us if the information above help you fix the code. What are the symptoms on your vehicle for the P0420 Subaru code? Have you replaced any parts?
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