O2 sensor Question OBD2

[203CT]

If the secondary o2 that goes under the car comes before the cat can it cause the computer to throw a code for a dismalfunction in the o2? I think my new cat is welded on backwards but I wanted to ask here before I go and get it re-welded.

[H22SteakSauce]

Yes

[203CT]

Yes

Thanks

[LS/Vtec]

so your cat is placed after the primary and secondary o2 sensor?

[d@_b3st]

Idk but usually the second o2 which is bank 2 is right in the cat , just at the end of the down pipe, is it backwards really?

[kevin]

secondary 02 should be behind the cat. never seen it in front.

[CTgoldhatch]

You need to have one sensor befor the cat and one after the cat. That main reason for the sensors is to read and monitor the changes in the exhaust gas as it pass threw the cat. So I you have the cat behind both sensors then the cat might still be working but the ecu won't know that is will eventuly throw a light for inefficient cat.