In an automatic wash, a control unit operates a boom arm around a vehicle in a bay by moving a bridge along a lengthwise vehicle orientation, moving a trolley on the bridge along a widthwise vehicle orientation, and rotating the boom arm about the trolley. The boom arm is coupled to a mount which is flexibly coupled to the trolley such that boom arm impact displaces the mount and the trolley. The displacement may be two-dimensional and/or angular. In response, the control unit determines whether an impact has occurred by comparing the data to a baseline. If there is an impact, the control unit relocates the boom arm and may continue the wash process. If a sufficient force impact occurs that the control unit cannot correct, the boom arm may disengage from the mount which may trigger a breakaway sensor and cause the control unit to abandon the wash.