Two Different Upstream O2 Sensors?

[murkinstock]

Hi, so I'm just curious. I bought new upstream O2 sensors, and they are different for the right and left. They're Bosch Part #s: 13117 and 15664.

Any idea why Bosch did this? My factory ones both appeared to be the same as the 15664.
I thought maybe it was an error with the parts store, so I checked Bosch's website and it in fact states one is for the left, and one for the right. I have done research and can't seem to find anything and wanted to see if any of you knew, or if maybe I'm misunderstanding something?

They have been installed for about a week now, and no apparent issues.

Thanks!

 

[koda2000]

Sometimes it's just because the wires are a different length.

 

[murkinstock]

Sometimes it's just because the wires are a different length.

Yeah, but these are actually a bit different. One has a lot of smaller holes, and the other a few bigger ones.

My only guess was it had to do with different flow characteristics, or amount of heat between the left and right, and they found that making one with smaller holes would improve accuracy.