I just replaced the O2 sensor behind the cat on the passenger side. I was told to check the fuse as well. The truck is a 2006 GMC Sierra 2500 HD. I have no idea what fuse needs to be checked. I can't find it in the manual either.
Fuse location or fuse number on 2006 GMC Sierra 2500 HD
underhood fuse box 02a and 02b 15a