0420 refers to Post O2 sensor under the car on passenger side. I got mine from Autozone about 70 - 80 bucks for a bosch. Not that hard to replace, takes about an 30 mins to an hour if you already have parts and car is cooled off.
P0420 is for a bad catalytic converter. If the downstream o2 sensor was bad, there would be a different code.
Leave the MAF sensor alone. Cleaning it can screw if up if you don't use the right stuff.
of course you use MAF cleaner, what else would you use? Dawn or palmolive? lol!
yo ucould have an vac leak, faulty injectors, spark plugs, exhaust leak, etc, etc.
Is there another code with it or is this the only code thrown?
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.
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