Toyota Repair: P1133 and P1135, air fuel ratio, o2 sensors

Question
My wife's 99 Sienna CE had check engine light on. The error codes are P1133 and P1135. Is the repair under powertrain warranty? If not, how easy to change A/F  sensor myself? Which bank is it at? Do I need special tool to replace it? Are the O2 and A/F sensor the same?

Thanks a lot

Answer
These are both air fuel ratio sensors, the warranty is normally 3yr/50,000 miles in some states.
These sensors are located in the exhaust manifolds, the front one (bank 2) is easy to get to, the one in the rear is more difficult, they require a special socket to remove and install. The O2 sensors are located behind the catalytic converter and are not the same as the A/F ratio sensors.