I can only help you by telling you that it's a yaw damper, and AFAIK, it's supposed to assist you with crosswind flying....

If you are refering to the YAW damper not working.
I have discovered that there is an entry in the aircraft cfg file that handles this.
Look in the Autopilot section usually at the bottom of the list you will see a line that looks like
Yaw_Damper=0.0000
Or something like that just chage the first 0 to a 1 and that should solve your problem
Yaw_Damper=1.0000
I found out when a panel is alised to another aircraft the YAW damper might not engage.
And the reason is what I stated above I found this out by comparing aircraft cfg files. I discoverd that the plane whose aircraft cfg file had the zero's in the Yaw Damper line the yaw damper would not work. 8)