I need two O2 sensors for my 1997 Rav4. I searched online to get a pair of sensors and came across www.oxygengeeks.com. They have a good informative about O2 sensors and their differences. My only concern was for my Rav4. According to this site, Toyota and Honda have what is known as an AFRS ( Air Fuel Ratio Sensor). It works like an O2 sensor but is cunstructed differently.
This threw me for a loop until I kept on reading. If the number on the sensor, or sensors, started with 98467 then it was an AFRS, if it started with 89465 then it was an O2 sensor. Not all Toyota and Honda cars have this sensor.
My problem? My sensors don't have markings inscribed into them. They are original. The little tags that are on the wires of the sensors are faded beyond measure. How do you tell if you have an O2 sensor or an AFRS when there are no identifiable markings? is there a color code on the wires or is there a physical diference? Both sensors are a two wire design and they are blue and white on both sensors. I thought I'de give this site a shot for answers before I called the dealer. I asked else where to widen my luck for an answer.  

wow! thats a bit of a pickle. if it's the stock sensor why don't you just head down to your local Napa or whatever you have and get them to tell you. I deal with Napa often , partially cause i get stuff just about at cost, and they are always able to get me what I need  

I tried them at first and they couldn't tell me the difference. Since posting this thread I've found out that my Rav4 has run of the mill O2 sensors. The AFRSs that I was reffering to are for the newer vehicles starting around the year 2000 and up. I purchased them on line through AUTOPARTSWAREHOUSE.COM. They treated me really, really well. I got the most incredible service. I use them for other things too because of their service. PARTSBIN.COM is theirs as well.  

oh, well thats good  

lol! I sounded like a spokes person for them, didn't I? lol! They were very good to me, though!  

before or after the cat?  

Both! And the cars that have those AFRS O2 sensors are on Toyota and Honda models. No other Japanese cars have this, from what I understand.
I have the sensors in my garage. I haven't had time to install them yet because my brother has my Rav4. I've been working on his car and just recently finished fixing the A.C. problem on his 98 Ford ZX2. Cool little car. Lots of pep. It's got a 2.0 ZETECH engine, dual overhead, 145hp, manual trans 4banger! It's got 145hp because I installed a few things and tuned it a bit. It helps when you work for a Ford dealership. LOL! Again, for what it is, it's a cool little car. And it's great on gas too! Who would have thunk?!