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Q: O2 sensor on exhaust it upstream or downstream...09 Nissan Altima

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Service Engine Soon light is on and I am getting the Catalytic converter replaced. I just need to know which O2 sensor to buy ? Upstream or downstream ?

My car has 21400 miles.
My car has an automatic transmission.

A: Hey there, thanks for writing in about your...

Hey there, thanks for writing in about your 2009 Nissan Altima. The downstream O2 sensor is the sensor used for catalyst efficiency. It is not the one in the manifold but the one after the converter. If you need help with an oxygen sensor replacement, our technicians can come to your location to install the correct the part.

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