95 850 glt problem with mph and km

Here is the deal....almost once a year my car goes back to the km setting instead of miles per hour setting. I have taken it back to the dealer almost every year since 1996. Is there a way through the control modules A and B under the hood that I could do this myself. The last time it was done, the dealer put a hand held device in the B module to reset back to the US standards. I have to take time off of work to go to the dealer to get this reset, its time consuming and costly. any help is greatly appreciated.