In transaction /DBM/WTY1 you can create warranty profile for maintaining warranty items which is used also in vehicle master tc /DBM/VSEARCH.
You can assign items with warranty control (WTY_KIND) <> 1 (vehicle warranty), but system allows only to add items from warranty profile with warranty control = 1 because only vehicle warranty items are valid in vehicle master.
Warranty profile maintained with item warranty control <> 1:
In vehicle master you can only add items from warranty profile where warranty control is set to 1:
Please consider this check.