However, DON'T include the depreciation on the amended forms.  Just amend to correct any interest deductions.  Only use Form 3115 on the current year return for the depreciation.

But as Lisa pointed out, if the rental is truly at less than Fair Rental Value (such as for family or friends), it may have been reported semi-correctly.  But if it is just low because the taxpayer doesn't increase rent and the renter is not a friend or family, it still might be considered a for-profit rental on Schedule E.