HI all: I was working on a 96 Cadillac with a 4.6 L and it has an O2 sensor for each bank and one before the CAT and one afer CAT. If the PCM uses Bank 1 sensor 1 and bank 2 sensor 1 for fuel control, what is the pre CAT (bank 2 sensor 3) used for? Is it a bac... Login to read more.