4WD Warning light illuminated during normal driving. 4WD system inactive creating unsafe driving condition in Michigan winter weather. Vehicle taken to Jeep Service center and found C1494-92 active fault code. Performed PTU fork recalibration and fault went away, vehicle returned to owner. Within 2 days, 4WD Warning light illuminated again. 4WD system inactive again creating unsafe driving condition in Michigan winter weather. Vehicle returned to same Jeep Service center and same C1494-92 active fault code found. Now fix changed to PTU replacement, very expensive and time consuming service. From first visit to second visit, warranty expired so customer was responsible for PTU replacement cost.