There are two variants of the RM - F04 remote control as used with the HD and HDR T2 units. It might also be relevant to the RM-F01 as used on the Foxsat HDR, awaiting confirmation.
To check which variant you have remove the battery cover and look for a white label:
If label states - MDB 1.3 then 3 digit code.
If label states - ADB 1.0 then 4 digit code.