02 sensor trouble code p1151 do I need to replace?

[Charming007]

I have a 98 mustang Gt and recently got this trouble code :

P1151 - Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2

Does this mean i need to raplace the 02 sensor if so which one left or right?

Or is it better to replace both upstream 02 sensors, or all four sensors @ the same time?

what does " Bank No.2 " mean anyways?

Any help would be appreciated thanks