Fault codes covered
79-01
This fault is set when the controller is unable to mount or access the USB drive. Conditions include failure to mount the USB drive, failure to switch to the mounted drive, expiration of the mount timer, or inability to open required software files (.bex for PCM or .dat for VFD).
The most likely cause is the USB drive not being fully seated, incompatible, or improperly formatted. It is also possible that the USB drive has missing or corrupted software files
Remove and re-seat the USB drive. Verify the USB drive is approved, correctly formatted, and contains the required files. Retry the operation with a good USB drive if necessary.
NOTE: Best results will be obtained by using a USB memory device that is between 4GB and 32GB in size and formatted as a FAT32 device. Any other formatting (NTFS, exFAT, etc.) may result in an error.
Source: ACHPVSR454-02SM troubleshooting pages.