Hello Sivahari
Good day!
The FS_OSC_DRIFT fault (SM48) corresponds to the monitoring of the independent fail-safe oscillator used by the FS26 fail-safe state machine. According to the FS26 Safety Manual, this mechanism is implemented within the ASIL D fail-safe domain.
You can find this representation in Figure 8. Safety architecture.
I hope this information has helped you, please let me know if you need help with anything else.
Have a great day and best of luck.