Sold my 2004 Rubicon, guy drove off and came back saying the speedometer didn't work....never had a problem before. The guy was a used car salesman and our first thought is he unplugged something because he immediately offered 2500 less and said he'd still take it. Sending unit at transfer case is fine, speed gear is fine, wiring looks fine. Found a fuse unplugged but didn't fix it when plugged back in. Get DTC p1692 which tells us nothing because there are no other codes. What could he have done to make it not work or what else are we missing? Thanks!