does it stop back feed ?

Depends on where the resistor is and what it's used for. Can you give us a diagram?
Taking a totally uninformed guess, it may be to stop the source of the switching current being pulled to ground..or it could be an open collec....oh. VW, not electronics. Sorry. Diagram please :P

Anyway, you usually use a capacitor to help with damping spikes and smoothing off abrupt terminations of power. Resistors provide balance to the force :vader

Some times they put a multi mega ohm resistor across the relay coil, because it, as coils do, generates a spark when its field collapses. this resistor grounds the spark, while not allowing any significant current flow under normal operating conditions.

Are you sure it's not a diode?

I was taught to use diodes for spike suppresion, though I can't think of any reason you would need to use this on a vw

I tend to use capacitors. They soak up all the surging electrons. That's on the main current, not the switching current. Put a cap across the switching pins and it may be a while before your relay turns off.

It's just occured to me that it could be there to prevent radio interference from the switching contacts.