CEL 18901 Lambda probe before cat

Red-i · 02-15-2022, 09:12 AM

hey guys,

Just noticed this code today. Lambda probe before catalytic converter, dynamic: slow reaction

I cleared the code in bm3, but i believe this is the o2 sensor before the cat, and i'll assume the code will probably come back.

I still have warranty with bmw. if the code comes back, not quite sure how to handle. flash back to stock and lock the dme, bring it into the dealer etc. I realize that the dealers can tell if the car's tuned. no point in hiding that. at the same time, I assume a bad o2 sensor cant' be blamed on having a tune, but really not sure.

or do i just go to an independent and have it addressed there.

any advice would be appreciated

oem.plus_440gc · 02-15-2022, 12:54 PM

Be careful about bringing the car to the dealer. Your DME will likely be updated and relocked and will not be able to be flash tuned again.

Red-i · 02-15-2022, 07:16 PM

Quote:

Originally Posted by oem.plus_440gc

Be careful about bringing the car to the dealer. Your DME will likely be updated and relocked and will not be able to be flash tuned again.

Yeah that's what I'm worried about. I think the latest firmware isn't unlockable even with a bench unlock?

I did drive home pretty aggressively today and the code didnt come back on but I don't know if that means anything

Wires · 02-15-2022, 09:49 PM

If they think it's tuned, they won't warranty that. They can draw a nice clean line between more boost, more power, more heat = O2 failure. And you'll get the joy of a locked DME and non-tunable car.

It's an easy part to swap. I think you can do it without dropping the downpipe (don't quote me on that). It's a joke to replace when the downpipe is out though.

Red-i · 02-15-2022, 10:15 PM

Quote:

Originally Posted by Wires

If they think it's tuned, they won't warranty that. They can draw a nice clean line between more boost, more power, more heat = O2 failure. And you'll get the joy of a locked DME and non-tunable car.

It's an easy part to swap. I think you can do it without dropping the downpipe (don't quote me on that). It's a joke to replace when the downpipe is out though.

Thank you sir. Appreciate the feedback.

Was googling around on swapping the o2. Didnt find a straight how-to. But I believe the airbox has to come out and it's accessable from the top?

Wires · 02-20-2022, 05:35 PM

Quote:

Originally Posted by Red-i

Thank you sir. Appreciate the feedback.

Was googling around on swapping the o2. Didnt find a straight how-to. But I believe the airbox has to come out and it's accessable from the top?

Yes, but that is stupid easy. It just pushes down on rubber grommets.

Find a video on how to swap your downpipe, that will get you all the info you need for this.

Quick question, are you getting a CEL, or just a silent code in the background. Sometimes glitches happen, and it will log a non-persistent code (IE not a full failure).

Red-i · 02-20-2022, 10:40 PM

Quote:

Originally Posted by Wires

Yes, but that is stupid easy. It just pushes down on rubber grommets.

Find a video on how to swap your downpipe, that will get you all the info you need for this.

Quick question, are you getting a CEL, or just a silent code in the background. Sometimes glitches happen, and it will log a non-persistent code (IE not a full failure).

It was an actual cel. Not sure when it showed up because the top of the steering wheel aligns right in front of it so I may have not seen It for a day or two.

But I cleared it with bm3 app and it hasn't come back yet.

alexander7599 · 02-21-2022, 12:39 AM

Please don't take it to the dealership… don't let them win.

khj24 · 03-29-2022, 03:34 PM

Quote:

Originally Posted by Red-i

hey guys,

Just noticed this code today. Lambda probe before catalytic converter, dynamic: slow reaction

I cleared the code in bm3, but i believe this is the o2 sensor before the cat, and i'll assume the code will probably come back.

I still have warranty with bmw. if the code comes back, not quite sure how to handle. flash back to stock and lock the dme, bring it into the dealer etc. I realize that the dealers can tell if the car's tuned. no point in hiding that. at the same time, I assume a bad o2 sensor cant' be blamed on having a tune, but really not sure.

or do i just go to an independent and have it addressed there.

any advice would be appreciated

Hey did this code come back for you? I have been having some mild stumbling the last few times I drove the car and saw this code when checking. Did you have any symptoms or did you read codes randomly?

G.Newt · 03-29-2022, 06:16 PM

Quote:

Originally Posted by khj24

Hey did this code come back for you? I have been having some mild stumbling the last few times I drove the car and saw this code when checking. Did you have any symptoms or did you read codes randomly?

Replace the pre-cat o2 sensor.

khj24 · 03-29-2022, 07:18 PM

Quote:

Originally Posted by G.Newt

Quote:

Originally Posted by khj24

Hey did this code come back for you? I have been having some mild stumbling the last few times I drove the car and saw this code when checking. Did you have any symptoms or did you read codes randomly?

Replace the pre-cat o2 sensor.

I wouldn't have a problem doing that, but I've seen some cases where people cleared the code and it didn't come back. My sensor hasn't been touched in 18 months and most people have the code pop immediately after a DP change.

Red-i · 03-29-2022, 08:25 PM

Quote:

Originally Posted by khj24

Hey did this code come back for you? I have been having some mild stumbling the last few times I drove the car and saw this code when checking. Did you have any symptoms or did you read codes randomly?

It never came back. I had zero symptoms. I just happened to notice the cel on the dash.

G.Newt · 03-29-2022, 08:51 PM

Quote:

Originally Posted by khj24

Quote:

Originally Posted by G.Newt

Quote:

Originally Posted by khj24

Hey did this code come back for you? I have been having some mild stumbling the last few times I drove the car and saw this code when checking. Did you have any symptoms or did you read codes randomly?

Replace the pre-cat o2 sensor.

I wouldn't have a problem doing that, but I've seen some cases where people cleared the code and it didn't come back. My sensor hasn't been touched in 18 months and most people have the code pop immediately after a DP change.

For sure. Always clear the code to see if the problem is a reoccurring one or a one-off. Hope it doesn't come back! We haven't seen too many o2 sensors fail on these cars.

Red-i · 05-05-2022, 07:06 AM

Came back again after 3 months. Just cleared code. Dunno if it's worth replacing.... Yet.

BeFitty8_F32 · 05-05-2022, 09:34 AM

Quote:

Originally Posted by Red-i

Came back again after 3 months. Just cleared code. Dunno if it's worth replacing.... Yet.

Similar...

I have had the P0420 code flash a few times and clear on its own. All stock no tune.

I have since replaced my charge pipe and added the MHD MPPS tune. No CEL has appeared.

I already made plans and purchased a HF DP and will most likely replace sensors just because. New car to me and having fresh parts will make me feel better.

claytonap1 · 05-05-2022, 10:26 AM

Its a cheap and easy swap. Just purchase the lamda pre cat 02 sensor which you can purchase from trodo.com (i also replaced my post 02 sensor which i purchased off of ebay). I didn't have a code thrown but i was experiencing stuttering issues in every gear/driving mode which was due to a bad oxygen sensor. Once i swapped them out, car runs like a champ now.

Red-i · 05-05-2022, 04:50 PM

Quote:

Originally Posted by claytonap1

Its a cheap and easy swap. Just purchase the lamda pre cat 02 sensor which you can purchase from trodo.com (i also replaced my post 02 sensor which i purchased off of ebay). I didn't have a code thrown but i was experiencing stuttering issues in every gear/driving mode which was due to a bad oxygen sensor. Once i swapped them out, car runs like a champ now.

Thanks man in terms of swapping it out is it done by taking up the air box and going from the top

And would this be the right one https://partsavatar.ca/2016-2018-bmw...17404#OVERVIEW

Red-i · 05-06-2022, 08:27 AM

I ordered last night I assume it's the right one.

BMWILUVU · 05-06-2022, 02:29 PM

Quote:

Originally Posted by Red-i

I ordered last night I assume it's the right one.

Correct part. Airbox may be alil stuck/harder to pull straight out first time around. Helps to have an O2 socket in hand.

claytonap1 · 05-06-2022, 06:33 PM

this was my part (pre cat 02 sensor):

Lambda Sensor BOSCH 0 258 027 104

Quote:

Originally Posted by Red-i

I ordered last night I assume it's the right one.

Red-i · 05-06-2022, 11:14 PM

Quote:

Originally Posted by claytonap1

this was my part (pre cat 02 sensor):

Lambda Sensor BOSCH 0 258 027 104

Thanks

. I googled it but it's all UK references. Maybe different part number over there.

Install looks super easy from the top.

Red-i · 08-19-2023, 11:02 AM

Quote:

Originally Posted by Red-i

Thanks

. I googled it but it's all UK references. Maybe different part number over there.

Install looks super easy from the top.

Old thread but might as well say I swapped it and all good a year later

02-15-2022, 09:12 AM	#1
Red-i Second Lieutenant 80 Rep 223 Posts Drives: 2018 340i Join Date: Jun 2021 Location: Toronto iTrader: (0)	CEL 18901 Lambda probe before cat hey guys, Just noticed this code today. Lambda probe before catalytic converter, dynamic: slow reaction I cleared the code in bm3, but i believe this is the o2 sensor before the cat, and i'll assume the code will probably come back. I still have warranty with bmw. if the code comes back, not quite sure how to handle. flash back to stock and lock the dme, bring it into the dealer etc. I realize that the dealers can tell if the car's tuned. no point in hiding that. at the same time, I assume a bad o2 sensor cant' be blamed on having a tune, but really not sure. or do i just go to an independent and have it addressed there. any advice would be appreciated
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02-15-2022, 12:54 PM	#2
oem.plus_440gc Lieutenant 365 Rep 529 Posts Drives: 2019 440i XDrive GC Join Date: Oct 2021 Location: New Jersey iTrader: (0) Garage List 2019 BMW 440i GC xD [0.00]	Be careful about bringing the car to the dealer. Your DME will likely be updated and relocked and will not be able to be flash tuned again. __________________ Current: 2019 440i xDrive Gran Coupe - Alpine White, Coral Red Dakota Leather, 8AT, MSport, THP, BM3; 2015 X5 35i xDrive - Mineral White Metallic, Mocha Dakota Leather; Previous: 2015 Subaru WRX - World Rally Blue, Premium, FBO+Tune
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02-15-2022, 09:49 PM	#4
Wires Brigadier General 1665 Rep 4,910 Posts Drives: 2016 340i xDrive Join Date: Apr 2008 Location: Calgary iTrader: (0)	If they think it's tuned, they won't warranty that. They can draw a nice clean line between more boost, more power, more heat = O2 failure. And you'll get the joy of a locked DME and non-tunable car. It's an easy part to swap. I think you can do it without dropping the downpipe (don't quote me on that). It's a joke to replace when the downpipe is out though.
	Appreciate 0 Quote

02-21-2022, 12:39 AM	#8
alexander7599 Alexander Hartunian 60 Rep 95 Posts Drives: 2018 BMW 440i Join Date: Sep 2018 Location: Napa, CA iTrader: (0) Garage List 2018 BMW 440i [0.00]	Please don't take it to the dealership… don't let them win. __________________ 2018 F32 440i - Black Sapphire Metallic - KW Suspensions V1 \| VRP Intake \| VRSF Catless Downpipe \| Dorch Stage 2 HPFP \| MHD OTS Stage 2 E40
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05-05-2022, 07:06 AM	#14
Red-i Second Lieutenant 80 Rep 223 Posts Drives: 2018 340i Join Date: Jun 2021 Location: Toronto iTrader: (0)	Came back again after 3 months. Just cleared code. Dunno if it's worth replacing.... Yet.
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05-05-2022, 10:26 AM	#16
claytonap1 Private 79 Rep 72 Posts Drives: 2019 x3 m40i, 2017 340i Join Date: Jan 2020 Location: oxnard iTrader: (0)	Its a cheap and easy swap. Just purchase the lamda pre cat 02 sensor which you can purchase from trodo.com (i also replaced my post 02 sensor which i purchased off of ebay). I didn't have a code thrown but i was experiencing stuttering issues in every gear/driving mode which was due to a bad oxygen sensor. Once i swapped them out, car runs like a champ now.
	Appreciate 0 Quote

05-06-2022, 08:27 AM	#18
Red-i Second Lieutenant 80 Rep 223 Posts Drives: 2018 340i Join Date: Jun 2021 Location: Toronto iTrader: (0)	I ordered last night I assume it's the right one.
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