According to Au7o's research across NHTSA recalls, manufacturer TSBs, and owner forum reports, the 2006 Lincoln Navigator has 6 documented known issues, with 3 rated critical. The most serious are 5.4L 3V Triton Two-Piece Spark Plug Breaks on Removal ($200-$1,200 repair), Navigator Rear Air Suspension Bag/Compressor Failure ($700-$2,400 repair) and Air Ride Suspension Compressor Burnout from Air Bag Leaks ($400-$2,200 repair). Across all issues with published estimates, repair costs range from $100 to $2,400. DIY maintenance guides at au7o.io.