Here is the instruction on programming 3 button remote key for Mercedes Smart Fortwo 451 up to 2013 by using original SuperOBD SKP900 auto key programmer.
Instruction:
Note: Do follow every IGN ON & OFF operation.
Connect SKP900 with vehicle via OBD diagnostic socket
Select IMMOBILIZER
Connect SKP900 with vehicle via OBD diagnostic socket
Select IMMOBILIZER
Select Vehicle Brand: SMART
Select model: BR451
Loading
INFO: Remote will adapt when key programming finish
Select Immobilizer system
Choose OBDII adapter, Turn ignition ON
SKP-900 will display VIN/FIN code
Select PROGRAM KEY
Adapt 6 keys most
Turn ignition ON
Programming…
Turn ignition OFF
Turn ignition OFF
Insert new key. Turn ignition ON
Turn ignition ON