2002 bravad awd light on #2

so jul 2006 i had the transfercase encoder sensor replaced reprogrammed transfer case control module with updated program serviced transfer case added 2 qt autotrac 2 , this was done by a dealer , but i had no warning light then today i took it in to a mechanic, ( not a dealer ) he got a error code ,and couls not read a module , but he found that the battey was bad so he replaced it and tested again every thing it was ok so i drove it home , and no light, so later in the day i took it to the city about 16 miles away and when i was almost there the light came on . so after my job was don i drove home and no light at all , so any ideas is changing the oil in the transfer case the answer? need help here