o2 sensor, which one is which?

[jhenty]

So the code im throwing says bank 1 sensor one, which one of the o2 sensors is this refering to? thanks.

[Gregtrd]

So the code im throwing says bank 1 sensor one, which one of the o2 sensors is this refering to? thanks.

the exhaust manifold nearest to the firewall is bank 1, bank 2 is nearest to the radiator.

[Astro]

Be sure to see if you have air/fuel sensors or O2 sensors. My '00 had air/fuel sensors, but had O2 sensors put in by mistake which threw a CEL (thanks UPFD!). Thanks to Greg, I've changed those out and no more CEL!!!

[Jon11582]

Before the cat, its A/F if its cali spec, and its O2 if its not. I believe both specs are O2 sensors after the cat.

Location has nothing to do with it, I'm the original owner of my 2000 Solara bought in NJ and its cali spec.
The error code for the sensor will be different for O2/A/F pre-cat sensor failure in Cali spec and non cali-spec cars. Like Astro said, make sure you get the right one for your error code.