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Oxygen sensor install mistake, dont know order of wires

I was installing a post cat (rear) o2 sensor on a 2001 subaru legacy gt wagon (2.5L sohc) and I made a mistake. I pulled out the 4 wires of the old o2 sensor from the “pig tail” connector. It looked like they were supposed to be removed. Anyway, now I don’t know the order of the wires. What do I do now?

fyi I used a bosch o2 sensor (with smart link?) I got from a mainstream auto parts store.
I’m sure I’m not the only person who has done this, it’s funny because the directions state “DO NOT REMOVE PIG TAIL WIRES”–too bad I didn’t read the directions until after I made this mistake. ha ha.

You think this is funny? I don’t.

“We don’t need no stinkin’ directions.” Ha, ha. Good luck.

A replacement O2 sensor should be a simple matter of remove and replace. The electric connector should plug right in.

What did you buy?

Thanks for the warning. I might even remember not to do that if I ever do my own work again. Always write to us with mistakes, it’s what some of us should hear.

I don’t do everything wrong but I’d like to get it down below 40%.

The front sensor ‘plugged right in’ but the rear wires needed to be spliced in.

To all people that hopefully will chime in and help. I know there are generic sensors that have the wires spliced and no plug. I stayed away from them when I was shopping, but they were less money, so I can see one giving it a shot, now help the poor guy fix this.

@galant Thanks!

I wish I could bring it back. The car isn’t a daily driver, so I have time to fix the wire placement. If I peel back the electrical tape on the car’s 4 wires that go into the 4 connector pig tail thing, they each have their own color. Granted these colors didn’t match up with the O2 sensor I bought, nor did it have information about it in the directions. The O2 sensors did have a guide, but the color of the wires on my car were different than what they had in the guide.
I might have to take it into the shop for this, which I don’t want to do.

So the bosch o2 sensor has 2 white heater wires, a black signal wire, and a grey ground wire.

You need a wiring diagram for your car, which would tell you which wires were which. If you’re lucky, that will be enough to match up with the “guide” for the O2 sensor you bought.

Wiring diagrams are usually part of service manuals, which you can get from many sources. A good source for inexpensive, used manuals is

Good luck.

Or maybe a visit to the junkyard and restore the wiring to the original and get an OEM sensor.

After talking to a friend, here is what I’m going to try (after I finish the head gaskets I started this weekend). Use a volt meter, the signal should have .5ish millivolts and the heaters should have 12 volts. Hopefully this is accurate…