The rear oxygen sensor monitors the efficiency of the catalytic converter. If the sensor wasn't working, there would be a diagnostic fault code related to it. When there's a fault code related to converter efficiency, the sensor has to be working to detect that. You replace the O2 sensor when it isn't working and you replace the converter when it loses its efficiency.
Where the confusion comes in is when some mechanics want to replace both parts. That person has your best long-term interest at heart. We know that once the converter is replaced, if the sensor acts up later, you're going to be angry and call him incompetent because you have to make a second trip to the shop and spend more money. Rather than have to listen to an angry customer, experienced mechanics replace everything related that could cause more trouble in the near future.
I think I have the best approach. I tell people what is needed now and what could cause trouble later, and let them decide if they'd like to gamble on just replacing what is needed now. People who don't have busy schedules aren't as likely to be angry at having to take time to come back to the shop and they appreciate my trying to save them money. Busy people generally want all the bases covered to reduce the chance of having to come back.
If you're prepared ahead of time that additional work and parts might be needed, you're less likely to be angry if that comes to pass. At least you had the opportunity to try to save a few bucks.
Monday, December 30th, 2013 AT 12:58 PM