Yes, it's B2S1, here's all the numbers off ToyoDIY.

89465-53150 EX MANIFOLD 4, 5, 6 SIDE(B2S1)
89465-53190 EXHAUST PIPE(B2S2)
89465-53200 EX MANIFOLD 1, 2, 3SIDE, NO.2(B1S2)
89465-53210 EX MANIFOLD 1, 2, 3SIDE, NO.1(B1S1)

That's the one that's cramped towards the firewall. An O2 socket works good but you can also get it pretty easy with an open end box wrench or angled wrench/swivel if you remove the battery. The top is more likely the easier route, there's some other good methods in this link>http://my.is/forums/f87/need-help-removing-b2s1-o2-sensor-393232/

 

How do you know you need to replace B2S1? What was the actual code?

 

Good point Johnny, if it's a heater circuit malfunction then that's a no brainer but other codes may indicate an engine issue and maybe the O2 is doing it's job(not sure what DTC you have). Just hate to see something replaced if that's not truly the problem.
Btw, you can get a OE Denso universal for less than $40 and splice it in or you can get a PNP, all oxygen sensors are the same anyways, only reason they have different part numbers is because they are cut to a specific length and affixed to a connector. Here's a link if needed.
Denso OE Identical Automotive Replacement Parts - In Stock for Your Tune-Up!

 

Thanks Jason. I don't have the actual code but I trust my mechanic and that's what he said when he read it (wish auto parts shops still read codes). I figured it would be the O2 sensor though, those seem to go after a while..

Also told me I need to replace my rack and pinion for a small leak. I'm not sure I want to deal with that yet though since it's so expensive

 

advance auto will read your code. They do in FL anyway

 

I believe most auto stores in California do not read codes any more, at least for free. I think too many people were stealing them but not positive.

 

I know in Texas they will read the code but WILL NOT clear it any longer.