finding a bit location in program

I am using siemens S7-400 PLC. In one of my program i am trying to find the location of bit say db131.dbx20.5 to see how it is has been written/set. By using GO TO the location it does not show my anything.Even if i search it by bit or byte or word.I am thinking now that may be its status is related to some FB somewhere or based on some condition in some FB this bit location status is chagned.
What method can be used to find it , how the status of this bit is changing.

Is DB131 an instance DB or global DB ?

Hi,
If goto cant find then that bit is being addressed indirectly.
If it is instance DB then FB related to this DB is operating that bit.

If its normal DB then see in CALL STRUCTURE to find which FC is using that DB (you can use cross reference).

If it is a M bit then........
happy hunting (start bypassing) or last line of OB1 should be the logic to control that rouge bit the way you want it.