Why does my upstream O2 sensor look different from the one that I found on web as an exact fit?

Hi all,

Left is the upstream oxygen sensor already installed on the car (2011 Hyundai Sonata GLS 2.4L).

Center is the one I found on rockauto.com as the exact fit for 2011 Sonata with California emissions.

Right is the one showing my car conforms California emissions (at least I think it does).

The sensor installed looks like the one that is sold for Federal emissions.

I really need an advice which sensor should I buy. If I buy the one on rockauto.com, will it fit my car?


the picture on the left looks like the downstream and the rock auto picture is the upstream. look on rockauto and all the upstream o2 sensors look like the denso one.

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Thank you for the reply.

Actually, picture on the left looks more like upstream -but without California emissions. My installed downstream is OK and consistent with the one on rockauto (right image). Also, there are 6 pins on upstream and 4 pins on downstream. So, it is unlikely that I have downstream installed on my upstream location.

Probably, they put a federal emission sensor instead of a California emission sensor. But I never got an error code about that. My average mileage is very low by the way.

your best bet is to go to the dealer parts dept. and ask them and get the correct part.

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It looks like the O2 sensor manufacturer added a heat shield to the sensor.

You can see the hex for the O2 sensor


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Oh, I did not know it is a heat shield. Now, it makes much more sense to me.

So, I am gonna go with buying the right sensor with heat shield.

Thank you for your replies and helps, you saved me from buying a wrong part.

Save your paperwork proving the part you installed is Calif compliant. The Calif emissions testing techs usually do a visual inspection of the O2 sensors. BTW, if in doubt it would be a good idea show this info to one of those Calif emissions testing techs for advice.


You don’t have to live in California to own a C.A.R.B. compliant vehicle.

My daughter owned a Honda that was C.A.R.B. compliant.

And we live in Minnesota where there’s no emission testing.


Good point. My comment doesn’t apply if OP doesn’t live in Calif.