P1148 Nissan - altima se. how do check if circuit is open or shorted?

Question

The car is 2005 nissan altima showing codes p1148, p1168, p1031 and p1051 which all correspond to the af sensors. I have replaced the ecm, checked every fuse which are all good and cleaned out the sensor connections. Just need to know how to check this before buying the af sensors if needed. Thanks everyone and anyone!!!