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PDP disappeared from the dashboard.
You mean the web-based roboRIO configuration page?
But if the RIO was reset and the browser was not manually refreshed, the silverlight plugin won't match CAN devices to the treeview on the left correctly.
Can you just try a simple power cycle of the robot, and cleanly close/reopen the browser?
If the PDP is not red, then it has healthy CAN.
Battery voltage in the DS comes from the RIO, not the PDP, so that shouldn't be used as a clue for PDP.