what is the chance that codes P0431 and P0421 only needs the sensors replaced

Question

I just wanted to know what are the chances that sensor just needs to be replaced on the cata if the codes P0421 and P0431 are showing up?

Answer 1

P0421 Warm up catalyst efficiency below threshold

P0431 Warm up catalyst efficiency below threshold

The best way to do this is with a scan tool if the frequency of the rear 02 sensor is the same or near the same as the front then then it is the catalytic convertor.  The ECM monitor the front 02 sensor in comparision to the rear. When the rear reaches the same or near the same it codes a insuffficient catalytic condition.