Getting a P0136 and need to know exactly which sensor this is.
I know it's Bank 1 sensor 2, but based on searches, I'm getting mixed information. Some say it's before the cat and other say it's after the cat.

Based on this image, which one is it?
http://contentinfo.autozone.com/znet...01.jpg/1.image

What is the correct Denso part # ?
234-4603
or
234-4209

[EDIT - Answer]
Both are correct.
4603 is the OEM replacement
4209 is the Universal version replacement

 

B1S2= driver side bank, post-cat sensor.

make sure you don't have an exhaust leak before you replace the O2 sensor.

 

Based on the image though, wouldn't the post-cat sensor be referenced as 'sensor 3' and therefore be labeled as as a different code?

Any good recommendations on how to see if it's an exhaust leak, short of manually inspecting for obvious leak areas?

 

lol no, that's a generic autozone image and has no bearing on the LS400's exhaust setup. what I mentioned is true.

 

Understood. Taking your word for it.

When I start looking O2 sensors, I'm seeing them referenced as either upstream or downstream. A post-cat sensor sounds like a downstream sensor to me. Correct?

234-4167 the correct Denso part number for this sensor? (or seeing somewhere else that it's 234-4603 for the post-cast sensors)

 

upstream and downstream refer to the cat. upstream=pre-cat, downstream=post-cat.

 

I ended using Rock Auto.com to get mine. I am in PR and prices here are a bit wacky but I got 2 OEM Bosch downstream for $126.00 shipped. Auto stores were about $120 each and the dealer was $230 each.

 

But what is the correct part # for the downstream sensors? I can't seem to find anything online that gives me 100% confirmation that I have the right Denso part #.