O2 Sensor

My 97 Astro AWD V6 failed the e-check OBD-II test. It showed a A0420 code so I replaced the Converter. The Check Engine Light came back on the next day, when I checked it showed a P0137 code(O2 circuit low voltage, Bank 1 Sensor 2) so I replaced the Oxygen sensor behind the converter. The light came back on the next day and shows the same P0137 code. Which of the 3 sensors is it refering to when it shows (Bank 1 Sensor 2)? There is a sensor just below the manifoldand' 1 in front of and 1 behind the converter, did I change the wrong sensor? Any suggestions?

SHould be the one in front of the cat.

Oops, I meant the one behind the cat. Sensor 1 is in front. Check your battery ground.

My 97 Astro AWD V6 failed the e-check OBD-II test. It showed a A0420 code so I replaced the Converter. The Check Engine Light came back on the next day, when I checked it showed a P0137 code(O2 circuit low voltage, Bank 1 Sensor 2) so I replaced the Oxygen sensor behind the converter. The light came back on the next day and shows the same P0137 code. Which of the 3 sensors is it refering to when it shows (Bank 1 Sensor 2)? There is a sensor just below the manifoldand' 1 in front of and 1 behind the converter, did I change the wrong sensor? Any suggestions?

Bank 1 is on no one cylinder side. sensor 2 is second sensor back
It should be in front of cat sensor 3 would be behind cat.
But many things beside the sensor can cause a code.
Get a repair flow chart for it and go threw the flow chart.
Did you use oem type sensor or splice in type?
MT