I have this formula that works on a form.  It's in an unbound text box.
IIf([FRRotorsReplaced]="New",DLookUp("[FrontRotorPart]","[BrakePartsGroup]","[AssetGroup]='" & [AssetGroup] & "'"),0)
However, if I copy and paste this into the Field line of a new column in a Query, and give it a title...