1997 K1500 O2 sensor code P0141, which one??

Hi, I have code P0141 "O2 sensor heater circuit malfunction (bank 1 sensor 2)".

Any idea which sensor is number 2?? There are sensors in both exhaust manifolds and one after the cat. At I believe $90 a pop, I don't want to replace more than I have to.

Thanks for the help!

It is the one on the driver side after the cat.

Thanks!