Where is H02s (B1 S1) located at?,code obtained was P0031

Thanks Roy. I have checked A/F fuse , relay, any air leaks, faulty gas tank cap,etc but I was not able to check the A/F sensor connector and sensor itself using a Ohm/voltmeter because I could't tell its location. can you please be more precise of its location? because there are many sensors located in the back head. OBD2 report reads as follow : P0031 HO2S Heater Control Circuit Low (Bank 1, Sensor 1) Your quick feedback is highly appreciated because car is consuming fuel like hell!!!!!

it is the only sensor on the back exhaust manifold. Roy