From http://autos.groups.yahoo.com/group/HackTheIBus/message/7428:
Q: How to SET the clock via the i-bus?
GT telling IKE to set the time:
3B 06 80 40 01 0C 3B CB
GT –> IKE : On-board computer set data: Set Time = 12:59
3B = GT
06 = length
80 = IKE
40 = OBC Set data
01 = Time
0C = hours in hex, eg: 0C = 12
3B = minutes in hex, eg 3B = 59
CB = checksum
GT telling IKE to set the date:
3B 07 80 40 02 1B 05 08 E8
GT –> IKE : On-board computer set data: Set Date = 27/05/08
3B = GT
07 = length
80 = IKE
40 = OBC Set data
02 = Date
1B = day in hex, eg: 1B = 27
05 = month in hex, eg: 05 = 05
08 = year in hex, eg: 08 = 08
E8 = checksum