There are two belts. Here is how to change them both. Pictures included.
http://www.justanswer.com/questions/1qyrs-2004-scion-xb-change-alt-power
Scion xB was created in 2003.
change the oil
The 2010 Scion xB has 16 valves.
The 2004 Scion xB has 16 valves.
The 2014 Scion xB has 16 valves.
The 2006 Scion xB has 16 valves.
The 2011 Scion xB has 16 valves.
The 2012 Scion xB has 16 valves.
The 2008 Scion xB has 16 valves.
The 2005 Scion xB has 16 valves.
The 2013 Scion xB has 16 valves.
The 2009 Scion xB has 16 valves.