To replace the drive belt on your Toyota Previa, you must remove the serpentine belt from the pulley system on the front of the engine. The serpentine belt, or drive belt, controls the movement of all the pulleys for various engine components in the van. Make note of the belt path on the pulley system, because the belt must be replaced according to the exact belt path in order for the pulley system to work properly. When the drive belt looks worn, or the teeth are cracked or missing, you should replace it.
Place the socket wrench over the tension pulley on the front of the engine. There is a pulley in the centre of the pulley system that has a 19mm nut welded to the centre of it. This is the tension pulley.
Turn the pulley clockwise to release tension.
Slide the belt off the pulley system, and install the new belt. When placing the belt over the alternator pulley, make sure that the belt teeth sit in the grooves on the alternator pulley. Also make sure that the belt is centred on the Previa's alternator pulley; otherwise the belt could fail prematurely.
Turn the tension pulley clockwise to let the belt slide over the pulley system.
Release the tension pulley to apply tension on the pulley system.