Help with O2 Sensor

I've got an '04 2.4L 2WD Standard Cab, and I'm getting error codes PO420 and PO136. I'm checking the rear O2 sensor, and I've seen posts here that tell how to determine if the sensor is fried by using a DMM. So, I have 2 questions:

1) What leads on the harness should I be checking, and what should be the correct resistance reading?
and
2) What is the correct part number for this sensor? I pulled it, and it says it's Toyota part number 89465-04220, but when I check any number of oem suppliers, all the web sites say that part number does not exist .

If it's fried, I want to make sure I get the right oem replacement. Been down this road before with a 4Runner, and it was nothing but trouble with the wrong sensor...

Thanks for any help!

 

Don't know about the whole testing thing but if you got over 100K on the truck then replace the O2 sensors....mine had 2 sensors and I had the codes also. Denso makes the sensors for toyota so rather than pay thier high prices i went and got my denso sensors from rock auto....I was told by many many guys here if ya got the codes and you are over 100K just replace them both. I have never had another problem with emission codes since i replaced them...DO NOT buy Bosch sensors!!! They suck...i found out the hard way...

 

thanks for part numbers. big help!
the truck only has a little over 50K on it, so i don't understand why the sensor is shot.

 

Where is this ( short Trips )^^^ written at?

 

interesting stuff. thanks.
i don't have a scan tool, but i checked the resistance of the sensor, when cold, and then after running of about 5-7 minutes. the measurement ranged b/t 14 ohm and 18 ohm, a % change consistent with the voltage range indicated in the FSM. so, i'm sort speculating here, but maybe the sensor is working ok?