Ok solved!
The doWatch command helped a lot, I wrote it to the engineer's init field.
If the vehicle is a bigger one the situation works more accurate and you can believe the engineer is working on the vehicle. At the beginning I tryed this case with a Jeep, but with a Scud it's ok. ( fortunatelly I needed it for a Scud).
Thanks the hints
If anyone (beginner beside me) interested:
TRIGGER_1: When the Scud dammaged a certain amount, the engineer moves inmediately to close to the vehicle.
Condition: this and damage SCUDNAME > 0.1 (or something)
On Act: ENGINEERNAME commandMove [getpos SCUDNAME select 0,(getpos SCUDNAME select 1)-1]
TRIGGER_2: And when the engineer is close enough he repairs the dammage.
Condition: this and ENGINEERNAME distance SCUDNAME < 7
On Act: ENGINEERNAME playMove "MedicToCombat"; SCUDNAME setDammage 0.1
This trigger needs about 6 sec delay to activate (countdown 6), because it makes the average timing correct. If the distance value is lesser then 7, the trigger should not be activated, because depending on circumstances the engineer closes the vehicle variable distances. Without delaying the engineer may act the anim too early.
It is important to set the doWatch command for the Engineer.