The code P0420 on a 2001 Toyota Corolla means the catalySTSystem efficiency is below the threshold [of the allowed efficiency for emissions control]. In other words, the catalytic converter is reported as not performing its job as well as it should. More specifically the oxygen (O2) sensors before and after it on the bank.There is an O2 sensor both in front (upstream) and behind (downstream) the catalytic converter. Normally, these two O2 sensors will have different readings when the car is running. The upstream sensor should have a fluctuating oxygen level, dependent on the amount of exhaust being created and the engine's fuel consumption rate.
Shelton H
July 16, 2020
The 2001 toyota corolla p0420 code means the downstream o2 sensor reported that the catalytic converter is not as efficient as it should be
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