Interesting puzzle.
Looks like it might be representing the trip odometer distance internally as 1/32768ths of a km, stored in a 32 bit signed integer. That would allow a range of -2**16 km to +2**16 km.
64388 mi -> 103644 km
103644 - 2*(2**16) -> -27428 km
-27428 km -> -17042 miles
-17042...