Front and rear O2 sensor signal wires joined?

I was redoing some wiring this afternoon, and when I removed the loom from the bundle containing the O2 sensors I noticed that the black/blue wire from both sensors are joined into a single wire (also black/blue) leading back into the bundle. It doesn't look like the splice is factory (I bought the car at 50k miles). It appears that's the signal wire from each of the sensors.

The car had a narrowband O2 sensor (signal was tapped at the ECU though) and alarm installed when I bought it. I've never had any issues or CELs related to O2 sensors, but it doesn't seem like that's how it's supposed to be. Is this one of those cases of "if it ain't broke, don't fix it", or should I take a crack at rectifying this?

Sounds to me that if you don't have a code for the problem you may just want to leave it. You may open a new can of worms trying to make it "right".

CorkSport-Chris said:

Sounds to me that if you don't have a code for the problem you may just want to leave it. You may open a new can of worms trying to make it "right".

Click to expand...

+1

Maybe they share a ground? That definitely doesn't make sense but I wouldn't start cutting any wires unless you have a problem.

At first I thought it was a ground too... but every reference I can find says that the black/blue wire is the signal wire. I'm just going to leave it alone, but I'm still puzzled a) why someone would do that, and b) why it's not causing a CEL or anything.