Apr 12, 2018 · If you want to keep the O2 sensors on there for emissions purposes, then the original O2 sensors are going to be very tired and worn out by now even though they may not set a check engine light. There will be 1 or 2 O2 sensors before the CAT but I can't remember if that gen of 5.3L & 4.8L has one or two after the CAT as well.