OK. In the manual page 138, I have read :
"The data link is used when there is a necessity to correct the missile’s flight trajectory during the mid-flight leg. An active radar seeker, which provides fully independent missile guidance after a safe target lock, turns on the radar and uses high and medium pulse repetitions to detect and track the target."
So we have our answer. :D
Shame on me. (RTFM :p)
Thanks all ;)