Volvo Repair: O2 Sensor, volvo s80, bank 1

Question
Hello, how many wires are there on an O2 Sensor for '99 Volvo S80?  If the error code for that part is given that triggers the "check engine" light, should i replace both?

Answer
Lennie, I think that car has 4 02 Sensors.  I dont know off hand how many wires there are.  To know the correct one to replace, the computer would tell me front 02 sensor Bank 1 or 2. Or Rear 02 bank 1 or 2.  Everything on these is a pain to do and you pretty much have to lower the exhaust system to get to those.  Roger