Quoting Perfect Pass's installation manual:
"To check servo & servo power wire, with key off turn black knob on servo motor counter clockwise 3/4 of a turn. Now turn key on and black knob should turn clockwise about 3/4 of a turn as part of the auto tighten. If it does, repeat procedure, except this time hold black knob gently to apply some resistance to auto tighten. If it rotates with good strength then it would appear servo & servo power cable are fine.
If it does not rotate or just vibrates, then a wiring phase coming to the servo maybe loose or broken. Inspect all wiring around servo. Pull both white plugs apart at servo & inspect pins to ensure they are in place. Gently tug on each wire to ensure they are securely in crimp. Check at mast Module where cable is connected"
"If motor does not wind in, but simply vibrates for 5-6 seconds, the servo power cable at Master Module may be plugged in upside down or a connector at servo motor may be damaged."
"If you cannot locate problem, contact Perfect Pass. 902-468-2150"
I was going to add, it sounds like the Servo connector at the Perfect Pass master module has come undone. The connector is not very vibration worthy.