If it seems as though you cannot get the tank to fill completely on an 01 Sienna, it is likely that your gas gauge is not working properly. You are probably actually getting the tank full of gas.
The gas tank on the 2008 Toyota Sienna holds 20.0 gal..
The gas tank on the 2009 Toyota Sienna holds 20.0 gal..
The gas tank on the 2003 Toyota Sienna holds 20.9 gal..
The gas tank on the 2010 Toyota Sienna holds 20.0 gal..
The gas tank on the 2004 Toyota Sienna holds 20 gal..
The gas tank on the 2014 Toyota Sienna holds 20.0 gal..
The gas tank on the 2012 Toyota Sienna holds 20.0 gal..
The gas tank on the 2013 Toyota Sienna holds 20.0 gal..
The gas tank on the 2006 Toyota Sienna holds 20 gal..
The gas tank on the 2011 Toyota Sienna holds 20.0 gal..
The gas tank on the 2005 Toyota Sienna holds 20 gal..
The gas tank on the 2001 Toyota Sienna holds 20.9 gal..