Back window of VW Cabrio 2001 is broken/ Need replacement

Need to remove the inner door trim which will give you access to the window regulator and the glass.

You'll have to erase the fault code otherwise it'll stay in that car.

Mass air low sensors can be cleaned. If a new one was installed you should be ok as far as metering the air, sensor has very sensitive and fragile wires, and should only be cleaned by mass air flow sensor cleaner. Unless they left it unplugged, or the computer is not picking up signal from one dead out of the box. The all points check may have dislodged a vacuum line. But if you are at the dealer, they need to be answering your questions, after that 4K tune-up.

Have you had the flywheel ring gear checked out for worn or broken teeth this can can stop the engine turning over

Yes, you need to get a new cable at the dealership, if you get lucky you might find one in good condition in a junk jard.

The window regulator or plastic tabs attached to the glass is likely broken and will need to be replaced, if you can hear the motor running but the glass does not move. If you're handy with fixing cars, you can purchase a window regulator and change it out fairly easily by removing the door panel and swapping the regulator out. If the plastic tabs on the glass are broken, you will have to take it to an auto glass shop to have new tabs replaced on the glass.

you need to pull away the hard cloth trim in the corners to get to the back of the light clusters.take out the floor carpet first to be able to get purchase.

that has to be sewed in

Take out the radio. sometimes the code has been written on it. It also might be written on the owners manual.
If not, take the radio and your VIN (vehicle identification number) to the dealer with proof of ownership of the car.
If you are nice to them they just might give you the code. My local dealership gave my code to me like this.

vwvortex.com

honestly, its the best place to find parts for cabbys...

good luck.
you can always call the dealer or another vw shop and see if they can order one, but I suggest vortex.
its a messageboard, so you have to find the vw classifieds, and then cabrio.