t.mcginley.jr

Hi all,

I have a 2000 XJ with ~200k miles on it and the CEL just came on. P0138 and P0141, both relating to one of the O2 sensors. Specifically the heater circuit of the sensor I think. Anyway since I have a 2000 and it has Cali emissions or whatever there's 2 precats, 1 main cat and 4 oxygen sensors. 2 upstream of the precats and 2 downstream.

P0138 and P0141 both relate to Bank 1 Sensor 2, but which one is that? I know sensor 2 is downstream, but is bank 1 the front 3 cylinders, or rear 3?

Thanks guys!

CCKen

Here ya go. I even provided you with the NTK part numbers.

t.mcginley.jr

Thanks! You're the man

So it looks like I need a front downstream sensor. $39.79 on Rockauto, plus shipping, sweet deal.

t.mcginley.jr

Re-opening this for some more info.

So apparently one of the previous owners chopped off the harness connector for that particular O2 sensor and hard-wired the sensor in. The harness side has different colored wires than the O2 sensor (which has a black, grey and 2 white wires). Anyone have a wiring diagram for this?

I've also heard that you can't solder O2 sensor wires because it messes with the resistance... any insight on that?

CCKen

Here's a diagram and a connector pin out for 1/2 O2S.


The wires on the O2s are:


Black = Signal
Grey = Ground
Whites = O2S Heater (not polarity sensitive)


Soldering the splices is desirable.

t.mcginley.jr

Blown away yet again, thanks for the perfect info. Hopefully going to tackle this on the weekend, I'll have to strip some of the harness back and see where I can splice in.

BlueRidgeMark

Depends on whether you can solder correctly or not. Many people can't, so bad things happen. These people then tell other people about the bad things that happen, and then an urban legend is born.

A common error that would wreak havoc with any sensor is what is known as a "cold solder joint". Basically, you get it just hot enough to flow a bit, glob things together, and think you have done a soldering job.

But a cold solder joint presents high resistance. Not a good thing in a sensor circuit!


Done correctly, it's a good thing.

CCKen

Doing a butcher job crimping a butt splice is just as bad.

TheGreatGazoo

A little FYI bank one is always where Cyl 1 is.

CCKen

Sorry...They made me do it. LOL

BlueRidgeMark

Heh. Most people do that badly, too, hence the bad (and completely undeserved) reputation of butt splicing.

t.mcginley.jr

Thanks for the help guys, I'll make sure and solder it properly. I think what I remembered hearing was about the O2 sensor wires themselves are stainless and not copper, but that could just be hearsay.

And thanks for the tip, I assumed cylinders 1-3 were bank 1, but wanted to make sure. Most of what I work on are transverse mounted 4-cylinder and V6 engines in import cars, where bank 1 is facing the firewall. I was overthinking the simple straight 6 design haha