Volvo Repair: Emissions Check P1152 code on Volvo S80 (year 2000), volvo s80, 2000 volvo s80

Question
I have a 2000 Volvo S80 with 122K miles. It had a GM Transmission that failed and was rebuilt recently. A few weeks after that, the Emission Service Required came on and there were 2 codes 1152 and 573. The 1152 was diagnosed to be a Front O2 sensor. This was replaced by Firestone. A few weeks ago, the same 1152 error came back. Now Firestone says that the Rear O2 Sensor has to be replaced. Can you advise if the O2 sensors have to be replaced in pairs. Can I get instructions on replacing it myself. Firestone is charging a whooping $570 for this and have already collected it once. Is there any thing available on the web that will provide the repair procedure for replacing the REAR O2 Sensor?

Answer
Ravi, That car has 4 O2 sensors.  To replace the rear sensors its best to have a lift.  Basically the cat has to come down so you can acess the sensors.  Firestone is nothing but a bunch of butchers that probably used a garbage sensor in the first place.  I advise you to go to a real Volvo shop or Dealership.  Roger