56, 253-02, Check Customer or System Parameters, this was from another post here that was in a google search. I dont remember what this is but here ya go. clear as mud!
Google it. Lots of codes on line. I did it to my dads 2000 W900l, just google peterbilt code 54 and see what happens. I found mine in 5 min. And if its something stupid like start up parameter check fail or something like that reset the computer by disconnecting the battery for 5-10min or if it has a reset button do that.