Nox sensor and desulphurising

kis2012 · 09-28-2025, 08:03 AM

Hello. I'm working through an issue with my car. I hope someone can help.

I had fault codes for Nox sensor self test error and Nox sensor plausibility.
So I changed the Nox sensor for a new genuine OEM (I think) unit and these fault codes have not yet reappeared (200 miles).

Unfortunately, the NoX sensor in INPA was showing as having too high a value on the page pictured below.

Schubabshaltung (Number 3) is typically over 5ppm and the Lineares Lambdasignal (Number 4) takes 20 seconds+ to reach a value of 19.

According to bimmerprofs, this is out of spec.

Is the brand new OEM sensor duff, or can anyone think of a reason why the sensor would act this way, what might cause a high Schubabshaltung (fuel cut off overrun)?

Some info on how desulpurising works in case it helps someone in the future....

The car would not run the desulphuration of the cat using either INPA or ISTA but there is no error given, it just never starts the process.

Desulphurisation can occur passively, when you get the exhaust hot enough by driving in a low gear on the motorway (4k rpm) 600 degrees.
Or, the ECU will run an active process usingfuel to raise the exhaust temp. You jus initiate the routine using INPA and then drive on the motorway. 70mph in 6h gear s fine, as the active process will raise the temp to 600 degrees and you will see the content number fall.

This active process will not run if there is an issue with the NoX sensor.
I know this because mine was showing 6! ppm in fuel cut off overrun or Schubabshaltung but occasionally will show a figure below 5ppm and then the process runs until the NoX sensor reports something above 5ppm again.
I also stored the fault code 30EA before I desulfurised the cat using INPA.

fqlynx · 10-18-2025, 10:27 AM

Hi had an issue with my Nox sensor on my N43.

There's two main elements to the sensor, the control unit and the sensor.
If you look on eBay or similar, which is where I got mine from.

There are units, listed as new, but they're actually refurbished genuine BMW items, but the sensor is replaced with a new NTK one. Additionally you may have an earlier iteration of the control unit.

IIRC, I had version 3, the one I bought was version 5. So a newer version 5 control unit, plus a new NTK sensor. Seems to have helped. Had it fitted for two years now.

That was one issue, but the injectors are still a problem.

09-28-2025, 08:03 AM	#1
kis2012 Private 17 Rep 59 Posts Drives: BMW E93 Join Date: Apr 2017 Location: UK iTrader: (0)	Nox sensor and desulphurising Hello. I'm working through an issue with my car. I hope someone can help. I had fault codes for Nox sensor self test error and Nox sensor plausibility. So I changed the Nox sensor for a new genuine OEM (I think) unit and these fault codes have not yet reappeared (200 miles). Unfortunately, the NoX sensor in INPA was showing as having too high a value on the page pictured below. Schubabshaltung (Number 3) is typically over 5ppm and the Lineares Lambdasignal (Number 4) takes 20 seconds+ to reach a value of 19. According to bimmerprofs, this is out of spec. Is the brand new OEM sensor duff, or can anyone think of a reason why the sensor would act this way, what might cause a high Schubabshaltung (fuel cut off overrun)? Some info on how desulpurising works in case it helps someone in the future.... The car would not run the desulphuration of the cat using either INPA or ISTA but there is no error given, it just never starts the process. Desulphurisation can occur passively, when you get the exhaust hot enough by driving in a low gear on the motorway (4k rpm) 600 degrees. Or, the ECU will run an active process usingfuel to raise the exhaust temp. You jus initiate the routine using INPA and then drive on the motorway. 70mph in 6h gear s fine, as the active process will raise the temp to 600 degrees and you will see the content number fall. This active process will not run if there is an issue with the NoX sensor. I know this because mine was showing 6! ppm in fuel cut off overrun or Schubabshaltung but occasionally will show a figure below 5ppm and then the process runs until the NoX sensor reports something above 5ppm again. I also stored the fault code 30EA before I desulfurised the cat using INPA. __________________ 2007 E93 M Sport 325i N53
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10-18-2025, 10:27 AM	#2
fqlynx New Member 9 Rep 17 Posts Drives: E90 LCI 318i Join Date: Aug 2023 Location: UK iTrader: (0)	Hi had an issue with my Nox sensor on my N43. There's two main elements to the sensor, the control unit and the sensor. If you look on eBay or similar, which is where I got mine from. There are units, listed as new, but they're actually refurbished genuine BMW items, but the sensor is replaced with a new NTK one. Additionally you may have an earlier iteration of the control unit. IIRC, I had version 3, the one I bought was version 5. So a newer version 5 control unit, plus a new NTK sensor. Seems to have helped. Had it fitted for two years now. That was one issue, but the injectors are still a problem.
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