Toyota Repair: 99 Solara V6 PO125?, exhaust leaks, scantool

Question
The car had 1 DTC for O2 Bank1 Sensor1 Heater Circuit Malfunction (don't remember the code number); I cleared the code out and it came back the next day. So I picked up the B1S1 O2 sensor from toyota and replaced the back O2 next to the firewall.  I cleared codes, but the next day a new code emerged as PO125 insufficeint temp during closed loop. (can't remember if it said open or closed, i think it was closed).  Anyway what causes this code to trip?  Scanner troubleshooter said possible causes are degraded main 02, I assume the scanner ment B1S1 (which I replaced) , it also suggested probing 02 connector for power, I'm confused and need this light off in a bad way.  Thanks.

Answer
This code is normally a secondary code that comes on when the a/f sensor fails, normally replacing the sensor will eliminate both codes since the 125 is a direct result of the a/f sensor failure. Have you tried clearing it and see if it comes back again? A dtc PO125 by itself could mean that there is an exhaust leak, if the code keeps coming back and there are no exhaust leaks I would recommend having a scantool connected to check the operation of the sensor.