Engine Light On-1997 Blazer/Jimmy

I just purchased a '97 Jimmy with an engine light on at all times.I did a scan of the codes and came up with a 0140 (O2 Sensor Circuit No
Activity Detected) and a 0719 (Torque Converter/Brake Switch B Circuit Low). Does anyone know what could be causing these faults? (I am assuming the first is simply the O2 sensor) Any help or suggestions would be appreciated. Thanks!
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