P0155 & P0135...Help

[Majdelboy]

I have a 2000 Lincoln LS V8. I did a scan because the car was idling a little rough and my gas mileage was bad. The following are the 2 codes P0155 &
P0135 I got. I assume that I need to replace the O2 sensors to solve this problem? Are there 2 or 4 O2 sensors on the car? Any help is appreciated...txs.

 

[Quik LS]

P0135 HO2S Heater Circuit Bank 1 Sensor 1
P0155 Heated Oxygen Sensor Heater Circuit (bank 2, sensor 1)

there are four sensors - one pre-cat and post-cat per side.

weird that both go at the same time.....