I have a CEL with (apparently really common) codes P0420 and P0430, i.e. issues detected with both catalyst system banks.

My vehicle is a 2007 Toyota 4Runner (Limited, 2WD, 6-Cyl) with about 150K on it...AFAIK it has original catalytic converters and sensors. So I think no matter what, I want to replace the sensors and then hope/assume they last for another ~15 years/150K.

But I noticed on the parts retailer website that Denso offers both O2 sensors and/or air fuel sensors. So my question is: Do I have a choice between the two in my upstream/downstream banks, or are they meant for different places/uses/vehicles?

Retailer site URL for my car: 2007 TOYOTA 4RUNNER 4.0L/3956cc Toyota V6 Denso Products Oxygen Sensors Parts & Accessories | Summit Racing

Emission Info: 2007 Toyota 4-Runner Emission Info Sticker

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    For the 2007 4Runner sold here in the States, I'm only seeing a V6 (4.0L) and V8 (4.7L) options offered? The numbers I'm seeing for Denso V6 engine is: Upstream - (up to June 07) 2349051; (from June 07) 2349026; Downstream - 2344260. I'm only seeing them listed as "O2 Sensors". Commented Mar 8 at 20:37
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    great info fromPaulster2. You can also check under engine hood. Emissions sticker should state what catalyst and sensors are in your vehicle. Commented Mar 8 at 21:12
  • @Paulster2: yep...thanks. That was a typo...it's a 6-cylinder engine. I've corrected it in OP. Upon further poking about on retailer site, it appears the "Air/Fuel Ratio Sensors" are for upstream, and the "Oxygen Sensors" are for downstream. I see why, based on your response, there are two offerings for AFRs, but I am still not sure why there are three offerings for O2 when I enter in my car details.
    – AA040371
    Commented Mar 8 at 22:28
  • @BillSullivan: I'll go check that right now :--)
    – AA040371
    Commented Mar 8 at 22:29
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    Under Toyota- 2A/FS and 2HO2S. and 2TWC. This tells me your vehicle has 2 upstream air fuel ratio sensors and 2 downstream zirconia sensors for cat monitoring. 2TWC is 2 three way catalytic converters. Commented Mar 8 at 23:50

1 Answer 1


To answer your question- No you do not have a choice on which sensors go where. On your Toyota 2 air fuel ratio sensors go upstream and 2 narrow band sensors go downstream.The emissions label I directed you to describes the emission standards your engine is certified.

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