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Mike V.
Mike V., Infiniti Mechanic
Category: Infiniti
Satisfied Customers: 25176
Experience:  Factory trained to repair Nissan and Subaru.
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Infiniti i30: Hi, need to replace 2 O2 sensors on bank 1, cant

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Hi, need to replace 2 O2 sensors on bank 1, can't figure out if they're the ones before or after the catalytic converter. The Infiniti part numbers are HO2S1 - B1 front O2 sensor, and HO2S2 - B1 rear O2 sensor.
Welcome to JA! I am Carguy1 and I will assist you today.
HI there!
Here is a diagram of the O2 sensor identification, hope it helps!
Customer: replied 5 years ago.
Hello - this does not answer the question, as I've already looked at the diagram and cannot determine if the two sensors I need are upstream (before the cat) or downstream (after the cat).

Can you please tell me if the two sensors you highlighted are specifically upstream or downstream, thank you.
One is upstream on bank #1
The other is bank1 sensor 2 which is the downstream sensor on the same bank.
The ones I highlighted, if you look, match what you stated above on the original question.
Maybe I am not understanding what you are asking, but you need to replace the bank upstream and the bank one downstream.
Customer: replied 5 years ago.
Hi - I think I've been staring at the diagram too long, and I'm very sorry to keep asking the same thing over and over... The parts store offered the selection of the following 4 sensors - can you just tell me which numbers they are, I think that would be easiest?
#1. Front downstream (after converter)

#2. Front upstream (before converter)

#3. Rear downstream (after converter)

#4. Rear upstream (before converter)
#1 would be the HO2S2- B2
#2 would be the HO2S1-B2
#3 would be the HO2S2-B1
#4 would be the HO2S1-B1

Hope this helps you out. let me know.
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