While a vehicle position and azimuth determining system(PADS) slipping or sliding in-flight, the odometer velocity output will remarkably debase the system navigation precision. In this paper, the error between inertial navigation system(INS) and odometer was projected to a finite interval, and then, a real-time odometer default detection strategy was designed through making use of the weighted exponential smoothing, which detection time window self-adjusting according to the fault magnitude. A mathematic simulation result show that, as a short-time odometer fault appears, this detection method can effectively detect and give alert to PADS rapidly, then isolate odometer output by INS velocity. When fault disappears, this method can de-alert and recover to normal navigation status, which decreases the error accumulation, improves the system precision and reliability.