I had this problem on my 98 Concours. Very hard to diagnose because in my case the car would only be low with a load and only after driving for 100's of miles on the freeway ( slowly leaked down over time), once I restarted the car it pumped right back up for another 200 to 300 miles. Just about every rest area I would get out and it was down about 1.5 - 2 inches. The dealer kept saying no codes no problem, I found out this was not true. After they replaced the shocks and air line with no help at all they finally replaced the compressor and that fixed it.
Good luck.
Good luck.
