Same thing on my 2000 Tundra.  Dealership wanted something like$200 to
change it and suggested I change "both" since the second one fails
shortly after the first (to the tune of almost $400 total).  Not sure
which other one was was supposed to fail since there are four
installed.  Anyway, I went to Auto Zone and bought a Bosch replacement
for about $70 and replaced it myselt.  The Bosch I bought appeared
identical to the oem.  Since the new one was a "fits all" job, I did
have to splice the pigtails on the new one which wasn't a big deal.
That was several months ago and guess what?  The "other" one hasn't
failed.

John

Should be covered by the emissions warrenty (at least in
US).

http://www.acarplace.com/problems/warranties.html
"Every car sold in the United States comes with a warranty
you may not be aware of. It covers a variety of components
for up to ten years or 100,000 miles. This is a set of
"emissions warranties," designed to ensure that cars do not
pollute as badly as they otherwise would. It places the
burden of emission system reliability on the automaker, so
they have to find ways to make the car stay "clean" for as
long as they can, or pay to fix it."

You might try cleaning the connector at the sensor first then re-set the fault
codes.

 Gary W.

There was a TSP issued for that problem. Check at Tundrasolutions.com and
search for O-2 sensor or go to alldata.com and find it.