I think that the I.Status word contains all the .Underrange and the .PowerUp bits that appear underneath it in the RSLogix 5000 module-defined Tags.
The bit positions should be the same as are shown for Input Word 8 at the bottom of Page 44 of that User Manual.
As a practical matter you can use the explictly-laid-out .ChXUnderrange and .PowerUp sub-element tags in your logic.
I don't know the contents of the .Fault word. It's possible that it indicates a module self-test failure or something else that would be uncommon or difficult to test.