I'm missing the two nuts what size nuts do I need?
SOURCE: catalyst efficency below threshold P0420 2003 Corolla
should be a bolt on for service ability
SOURCE: P0420 and P0430
The AF sensors are uupstream and the O2 down stream. The car' s computer tests them and it is saying your cats are bad. If you have a scan tool you could look at the data and see what the sensors are seeing. The Af sensors are the ones that control the fuel ratio in the car while the O2's just watch. AF's would be the one to change but there is no garuatee that the codes won't come back.
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