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OK folks, there were three sensors on the powertrain car's exhaust. I don't think all three are O2, I think one is EGT.

Sensor #1 was in the headers. It has a rounded element with two slits in it. It has four wires coming out of it - grey, white, and two black. I think this is the EGT. Correct me?

Sensor #2 was in the downpipe. It has a cylindrical element with a bunch of small holes in it. It has what looks to be an OEM 4-pin connector on it. It has four wires - white, blue, and two black. Narrowband O2?

Sensor #3 is still in the midpipe of the exhaust. I can't see the element. It has five wires coming out of it - white, red, yellow, gray, and black. Wideband O2?

Let me know if my assumptions are correct. The only one I'm worried about is the narrowband O2 to get the car running. I found vrg3's post about the Bosch wire colors, but blue was nowhere on it. Any idea how I hook it up to the OEM harness?

Thanks!

--Andy

The one in the downpipe & midpipe are O2 sensors.

The downpipe is going to be narrow band. The rear....is usually used to monitor cat efficiency....and really isn't that important for the car's overall running. I couldn't tell you if it's a wideband or not.

Yeah, it sounds like the one on the headers is an egt sensor of some kind.

You don't say what the powertrain car is, which could be a very useful clue.

But anyway...

1 and 2 both sound like narrow-band oxygen sensors to me. Four wires with two the same color usually means a signal wire, a ground wire, and two heater wires. And most cars do have a narrowband sensor before the cat(s) and a narrowband sensor after the cat(s).

What part of the downpipe is sensor 2 in?

An EGT sensor would probably only have two pins.

Sensor 3 sounds like it might be a Bosch wideband oxygen sensor... Those are the wire colors that go to such a sensor. There's also a green wire, but that just goes from the sensor's connector to the ECU; it doesn't actually go to the sensor.

I don't know why they would put a wideband sensor downstream of the catalytic converters... Or was this a modified car that had no cats?

Can you take pictures? Are there any words or numbers stamped into any of the sensor bodies? Do the sensors have hexes on them for gripping with a wrench? If so, what size? Oxygen sensors almost universally have 22mm or 7/8" hex bodies.

These came out of Phil's/Edwin's old car... so yes, it was very highly modified (with no cats). Edwin has a 50 trim turbo on it at one point and I think it did close to 420WHP. I know he had a DTEC on it but I don't know what other EM/gauges/monitoring he used.

Sensor #2 was in the bottom of the TurboXS downpipe Edwin had on the car.

I can take pictures but I have to wait until tonight to upload them.

#1 has the following markings on it:

0 258 005 729
4910231 12V

It has a hex fitting.

#2 - the only complete number I can make out is 234000-9220. Also has a hex fitting.

#3 - "0 258 007 057" and it also has a hex fitting.

Pics will be up later tonight.

Thanks for the help guys!

--Andy

Oh, right, I forgot it was that car.

#1 is a Bosch narrowband sensor. Are these the stock WRX headers? Cuz they have an oxygen sensor bung that the stock wideband sensor goes in, and Edwin might have just plugged that bung with the first sensor he could find.

#2 is a Denso (I think) narrowband sensor. I think that's the stock sensor there.

#3 is a Bosch wideband sensor. Edwin must have added the bung down there just because it was easy to do and because there were no cats upstream of it anyway (right?). Unfortunately, without the calibration resistor that the green wire's attached to, the sensor won't be usable.

I have stock WRX headers on it now, but I don't see a bung for anything. They were from an 02 WRX.

Here are pics if anyone cares:







There may be a resistor somewhere in the harness between the sensor and that massive plug. I'll check next time I'm there.

So, I guess I can plug #2 into the bung on the bottom of the downpipe and wire it into the stock harness. Which wire goes where?

--Andy

Stock WRX exhaust manifolds do have an oxygen sensor bung. On outboard side of the passenger side manifold, where both sides' exhaust meet up. They had to put it there because it needed to be upstream of the cat in the uppipe.

The top picture definitely looks like a Denso narrowband oxygen sensor.

The middle picture definitely looks like a universal Bosch 4-wire sensor.

The bottom sensor definitely looks like a Bosch wideband sensor. It's actually intact! That weird bump in the connector houses the calibration resistor.

You can use either of the narrowband sensors with the stock ECU.

If you use the Denso, the blue wire is the signal, white is ground, and the two black wires are the heater.

If you use the Bosch, the black wire is the signal, gray is ground, and the two white wires are the heater.

Thanks for the heads up V. I'll check for that bung this weekend.

Which of the two narrow-bands would you use? I have no idea how long they were used, and they look about the same to me.

--Andy

The Bosch one looks a little bit better to me.