A serpentine belt or main drive belt on the VW Passat runs multiple accessories. On many V6 models, one serpentine belt runs the fan, alternator, power steering, water pump and air conditioner compressor. On a 1.8L four-cylinder engine, VW Passat models tend to have two belts. Volkswagon recommends checking the belts for wear every 6,000 miles or 6 months.
Take off all accessories as necessary. If your VW Passat has a V6 engine, it may have an engine cover that you need to remove before working on the belt.
Find the belt tensioner pulley and rotate it to release tension. The tensioner pulley is generally between the crankshaft and another component. You'll see it is not connected to a component and has a bolt in the middle. On the VW Passat, it can be tough to reach the tensioner. Some recommend a long 17-millimeter wrench.
Remove the old serpentine belt. Loosen the bolt and slip the belt off of the pulleys.
Look at the belt routing diagram to find out where to thread the new serpentine belt. If you can't find a routing diagram, sketch one out before removing the old belt. You may be able to find a diagram on the Dayco belt guide site. Note that the Dayco site only shows a belt routing diagram for some Passat models.
Install the new serpentine belt, making sure the belt is seated properly in each groove.
Take your wrench off of the belt to release the belt tensioner.
Run the engine and observe the belt, checking for correct installation. Replace the engine cover if necessary.
For correct removal and replacement of the engine cover, see owner's documentation. For a separate AC drive belt, you may have to remove a splash shield to work on the belt.