[ReeseGia]

Hello,

Recently my car popped up the lovely check engine light and upon reading it I got the code 12B304 lambda probe heating after catalyst activation: Line Break from BM3. The car is a 2016 435i x drive with a Wagner tubing high flow catted downpipe. Multiple technicians said it's the rear one after the downpipe but I wanna make sure. The part is about 80 dollars just to shut off a check engine light. Are there any workarounds such as cleaning the sensor or do I really need a new one? If so, anyone know how to do it.

Thanks in advance

[5w20]

I had the same exact code, the fix was installing a new rear O2 sensor.

On a side note, you’re trying to find a workaround on an $80 part that there’s simply no workaround lol.

[n55david]

I have the same issue. lol

I've never actually looked at how hard it is to do the rear sensor swap on an xdrive car. I feel like it's a pain in the ass... lol

[Munchi435i]

Its a BMW!! Pay the $80 and be done with it. No sense in bandaging the issue.

[thejeremyman9]

Originally Posted by Munchi435i

Its a BMW!! Pay the $80 and be done with it. No sense in bandaging the issue.

100% this. The secondary O2 is used for more than just cat monitoring, and we are talking about something less than $100. Fix it.

[ReeseGia]

Originally Posted by thejeremyman9

100% this. The secondary O2 is used for more than just cat monitoring, and we are talking about something less than $100. Fix it.

Any info anywhere on how to install it? I don't even know where the things located lol

[ReeseGia]

Originally Posted by ReeseGia

Any info anywhere on how to install it? I don't even know where the things located lol

This is the part right?

[5w20]

Originally Posted by ReeseGia

This is the part right?

Correct part.

With a catless dp, it was easy for me to loosen it from the bottom and just disconnect the electrical from the top. I’m RWD btw.

[ReeseGia]

Originally Posted by 5w20

Correct part.

With a catless dp, it was easy for me to loosen it from the bottom and just disconnect the electrical from the top. I’m RWD btw.

Did you go under the car for that? Also do I need a special socket tool? Thanks

[bellguy]

Extremely cheap and easy repair
Yes you need to go underneath and no you do NOT need a special socket as easy way is cut the sensor wire off and use a normal deep socket, not like the old sensor needs it’s wire is it

[rjd_F30]

$90 part and 30 minutes in the garage. I also vote fix it. No special socket needed, though an O2 socket is a nice thing to have.

[5w20]

You can rent the O2 socket sets from your local auto parts store.

[thejeremyman9]

Originally Posted by bellguy

Extremely cheap and easy repair
Yes you need to go underneath and no you do NOT need a special socket as easy way is cut the sensor wire off and use a normal deep socket, not like the old sensor needs it’s wire is it

This is true to remove the old one, but then how will you install the new one with the wire?

You should either get the correct O2 sensor socket with the slot for the wire, or make sure you have a open/box end wrench of the correct size than can access it. O2 sensor sockets are like $3-10.

[Muwiee]

If you wanted to verify you could also put in a spark plug non-fouler or 02 sensor spacer both for less then 10 dollars. I'm unsure if there's is space without looking but I had to do this on other cars that didn't have full catted systems. This pulls the o2sensor back out of stream. The secondary sensor post cat monitors emissions efficiency. The primary one pre-cat sets fueling air ratio. Although post cat if gets bad readings will tell DME to change fueling as well assuming you have good emissions. You've changed this as you know so shouldn't be issue. Now with you having catalytic converter on car it's possible and probable the 02 sensor is actually bad. Hard to tell without being at car and knowing more information. Good luck.

[thejeremyman9]

Originally Posted by Muwiee

If you wanted to verify you could also put in a spark plug non-fouler or 02 sensor spacer both for less then 10 dollars. I'm unsure if there's is space without looking but I had to do this on other cars that didn't have full catted systems. This pulls the o2sensor back out of stream. The secondary sensor post cat monitors emissions efficiency. The primary one pre-cat sets fueling air ratio. Although post cat if gets bad readings will tell DME to change fueling as well assuming you have good emissions. You've changed this as you know so shouldn't be issue. Now with you having catalytic converter on car it's possible and probable the 02 sensor is actually bad. Hard to tell without being at car and knowing more information. Good luck.

FYI you aren't supposed to run O2 spacers / mini cats / etc long term. Might be OK for a test but realistically this is more hassle than its worth. Just replace the O2.

[bellguy]

I personally was just explaining that you can cut the wire so as to use an ordinary socket to remove it as it has no further use.
If in difficult spot and I have no choice I will cut the wire off the O2 sensor, attach the wire of the new sensor to the wire of the old one and pull it through, then screw in new O2 sensor and fasten wire in place from underneath on my lift or from above whatever is required.
It still remains an easy job to do, half hour to 45 mins max.
Also the slotted O2 sensor sockets are all but useless if the sensor is megga tight as they splay open, I only use quality tools and even they are poor in this respect, and should that socket slip because it has splayed open, damage could be bad to both machine AND hand, I know well enough lol lol.

[Insane435]

I just got the same line break code for the downstream O2 sensor. What is odd, is that this is the second time I got this code in the past year and a half. Is this a coincidence? I replaced the first one with the Bosch part.

[ZM2]

Yeah, anyone else having issues with the FCP O2 sensor? Mine seems to be flaking out too.

[Insane435]

Originally Posted by ZM2

Yeah, anyone else having issues with the FCP O2 sensor? Mine seems to be flaking out too.

I just ordered another a replacement since they reimburse you. It just seems odd that the Bosch one died after 1.5 years and only 3000 miles.

[ZM2]

Originally Posted by Insane435

I just ordered another a replacement since they reimburse you. It just seems odd that the Bosch one died after 1.5 years and only 3000 miles.

I'm still in my 90-day return window, so may try an OEM sensor and return the Bosch for refund if the OEM sensor fixes the issue.

[Insane435]

Originally Posted by ZM2

I'm still in my 90-day return window, so may try an OEM sensor and return the Bosch for refund if the OEM sensor fixes the issue.

I would imagine the OEM one is made by Bosch. They look identical as well. Is it possible it is getting fouled or destroyed by burbles? I have my burble settings basically to nothing (0.3s duration, 4 agg) can't imagine thats causing it.

[ZM2]

Originally Posted by Insane435

I would imagine the OEM one is made by Bosch. They look identical as well. Is it possible it is getting fouled or destroyed by burbles? I have my burble settings basically to nothing (0.3s duration, 4 agg) can't imagine thats causing it.

My burbles are set to zero.

Could just be a bad one. Will have my shop take a look when it's back there in a few weeks for other work.