o2 sensor 8.1l

[454ss]

2002 hd with 8.1l, ses light came on so stopped at a-zone and they checked the code and said it was right side o2 sensor but couldnt say if it was front or rear,they said you always replace both, well thats bs. truck runs normal, tailpipe isnt all sooty and black like when ive had a pre-cat sensor fail in the past so im guessing the rear sensor is bad since its not affecting how it runs. opinions?

[Duelin]

Did they tell what the code was? If you have a code you can tell which sensor to look at. Could be different things causing an o2 sensor code to set.

[8.1HD/ALLISON]

Have you checked your o2s? Mine does not have post cat sensors. They are feeding you a line saying you have to replace both, however if it has been a long time it might not hurt. Could help fuel milage etc if they are starting to slow down.