upstream o2 sensor location?

[nicholasleimenstoll]

hi my name is nick...some people call me niko. i'm havin a problem locating where to the o2 sensor is in my 2010 chevy aveo5 lt. i took some photos mabye you guys can help me since i took some pics from my phone.

[xintersecty]

There is two, one before the cat and the second after the cat. The bottom picture shows the one after the cat. The one before the cat is under the heat shield.

[nicholasleimenstoll]

how would i know which one to replace....i thought there was only an upstream and a downstream ...not 2 upstream and 1 downstream.......where is the downstream one?

[xintersecty]

Before the cat <- upstream o2 after the cat downstream 02
This should help on understanding how things work: O2 Sensors: FYI - Eastern Manufacturing

[nicholasleimenstoll]

so is this the upstream o2 sensor in front of the heat shield......

[petrified.rabbit]

it is.. . . . . .

[xintersecty]

The one on the right is upstream, the one on the left is downstream. The thing in between is called catalytic converter. We call it cat for short. Here kitty kitty.