I have an exhaust tip re-welded on my exhaust and noticed the 02 sensors were mixed up (not criss-crossed, just the front back on each side were swapped)

I had a perfect tune (dyno/log etc..) and then I added a second fuel pump (in-line) and went with a catless exhaust. It was at this point my 02 sensors must have been switched. I relogged my car on pump gas and my tuner said they looked good (ie: no changes needed).

I have not gotten any warning lights on my car...not sure if thats because the O2 sensors are fine or because my software tells the computer to pass emissions even though there is no cat...

Does the order of the 02 sensors really matter? they have different part numbers, but it could just be because the length.

 

I had to switch mine it did bring up a code later on

 

Usually there is a difference between front and back, but when you go catless, the readings would be as if the two sensors were in the same place. Your tune must be cancelling the warning.