Replacing O2 sensor on 2007 dodge ram 1 bank 2

My dodge ram is throwing a code for the o2
sensor. (1 bank 2). I replaced the  downstream on
the left side ( but the red saftey  clip broke so I zip
tied it together) and it's still throwing the code.I
just had my entire exhaust and new catalytic  
converters  put on. Do I need to replace all of the
o2  sensors or would  there be a certain one to go
to and replace? I'm needing help cause I have to
have my inspection  done in 2 days and trying to
limit the ones I should look at to replace with out
buyin them all