Error Code came up with O2S Ckt Malfunction 1/2

I know it is an Oxygen Sensor, but which sensor is it?

Haynes Manual does not give any clues to which sensor is what.

I believe it should be before the catalytic converter.

Wanna make sure before I go to a friends this weekend and use his lift, to change it.

 

1/2 is probably 1 of 2 -the one ahead (toward the front of the car) is usually #1.