power locks not working 1998 golf
 

whenever i use my remote or the button inside the car to lock all the doors, only the drivers door locks/unlocks. the motor for the power locks in the back just runs for about 30secs- 1 minute. none of the other locks operate unless i lock/unlock manually. is there anyway to fix this? i know it is operate on air, but cannot find any info on it other than that. please help.