2000 4Runner A/f & O2 Sensors

[Rich Freeman]

Hello,

I have a 2000 Toyota 4Runner 4wd / AT / 3.4L / Calif. Emissions /SR5 and I'm wanting to change the A/F sensor (pre-cat) and the O2 sensor (post-Cat). Denso list the A/F sensor with 2 part #s 234-9001 & 234-9002. What is the difference and which one should I buy? I believe the rear (post-cat) O2 sensor is Denso 234-4153.

Any help would be greatly appreciated.

Thanks

Rich