Quick addendum - the procedures here are primarily those that currently have either non-existent documentation (in print), poor/inaccurate documentation, or documentation that could stand improvement. If you're interested in maintaining a car, having a service manual is essential to guide you through the basic procedures (oil & filter changes, for one).
There are two good sources currently available:
- Haynes: VW Passat & Audi A4 Repair Manual, $15 USD - The Haynes guide for the
Passat is surprisingly thorough and useful - especially if you haven't worked on a car before, as very little knowledge is assumed.
It's a good buy even if you're not interested in doing your own maintenance, as it'll provide a good foundation to understand
exactly what it is dealerships and mechanics are going on about (and help to catch them when they're trying to rip you off).
Widely available at auto parts stores (Pep Boys, etc) and online.
Cons: Wiring diagrams cover major systems, but not all. Does not cover niche repairs. Little in the way of bragging rights (the low price of the manuals equates to useless information to some. The same mentality sells bottled water, Bose loudspeakers, and unneeded premium gas).
For what it's worth, little of the work I've done in the past five years required a lookup in the factory manual. It's certainly nice to see the full breadth of information (and occasionally essential), but you can go a very long way with a Haynes manual and Google.
- Bentley - VW Passat Service Manual, $120 (paperback hardcopy) - The Bentley manuals contain procedures (often verbatim, but augmented) from VW factory service information. Very thorough, though pricey. This is the one to get if you'd like to see the entire car broken down into exploded diagrams, or need a very specific procedure not covered by Haynes (computer diagnostic procedures, in particular).
Note that the Bentley VW Passat Repair Manual on CD is not recommended - documentation is taken directly from VW factory service information and dumped onto CD, without elaboration or explanation of procedures. Navigation is terrible, printed out pages have low resolution (read: fuzzy) images. Not much of a problem for mechanics and VW factory techs, but seriously lacking for the owner who wants to learn about their car.