Possibly you noticed some suspicious symptoms, which can suggest that there are some problems with the engine – increased fuel consumption, the engine has become “clumsy”, idle is more unstable, vibrations can be felt while driving.

Possibly, you performed the test of Stratified charge as described here.

If you have found this entry of the blog, most probably – you have detected that the engine does not use a Stratified charge. In this entry, I will explain what you have to do to find, where the problem hides. I deliberately use the term “hides”, because DME of F series hides a lot of problems – it does not record the error messages; BMW has turned off the access to many data, which makes the diagnostics of these complicated engines very hard.


Note: procedures, mentioned below, are up-to-date if the car has an OEM NOx sensor installed.


For the diagnostics of the problem, the following tools are required:

  • ISTA D/+
  • INPA for F series; MSD87 loader 3.700


Of course, if the DME error message list contains the error messages (even as if not connected – regarding oil or fuel pressure, cooling blinds, water-pump, EGR, ect.), the problems have to be solved! These DMEs have no insignificant problems. So I move to the scenario – no error messages in the DME error message list, but the engine warmed up till work temperature does not use a Stratified charge.


1. Re-adapt the engine. Description of the procedure here.

Note: for deleting of the adaptations, use ISTA D/+ only! It is important! ISTA D/+ deletes adaptation learnbits and values of all systems, except contamination of the NOx catalytic converter.

Check, if the Stratified charge is restored. If the Stratified charge is restored but after a certain time (5 .. 15 .. 25 minutes) or in the next driving session is turned off for a longer time (more than 5 .. 10minutes), there is a high possibility that:

the NOx sensor has a hidden defect, which results in the inability of the sensor to perform a self-diagnostics. Description of the problem here.

Unfortunately, nor INPA, neither ISTA D/+ does not allow to access the live data of the sensor, to make 100% sure regarding the problem. Solution: replacement of the NOx sensor.

If the Stratified charge, however, is not restored, possible cause of the problem: contaminated NOx catalytic converter or its performance is reduced. Unfortunately, in none of these cases, DME will record any error messages (in case of contamination – there is not even an appropriate error message in the error message map). Full list of possile issues can be found here (2nd part of entry).


2. Try to perform the cleaning of the NOx catalytic converter. Description of the procedure here.

If the desulfation session starts successfully and the level of the contamination of the NOx catalytic converter drops, it’s a good sign. At least in this driving session, the NOx sensor sends data.

After desulfation session – restart the engine and check repeatedly, if the engine has restored the Stratified charge.

If the engines do not switch on the Stratified charge, or after a short moment (during several minutes til several tens of minutes) turns it off for a long time, or in the next driving session the problems with Stratified charge continues – obviously, the NOx sensor works unstable and stops sending of data periodically.

Note: short-term stop of the Stratified charge (till 5 .. 10 minutes) is normal. During these stops, the engine performs specific service procedures (trim of Lambda probes, proceed LTFT, TEV, EGR, etc. component tests). But, if the Stratified charge is not restored after 5 .. 10 minutes – there is a problem.

If the desulfation session does not start, evaluate the contamination of the NOx catalytic converter (../F6/F2/F5):

  • if the contamination is above 1000mg, definitely – the NOx sensor has a hidden defect, it has to be replaced;
  • if the contamination is 500 .. 1000mg, repeat the desulfation session, increase the driving speed till 130 .. 140km/h. If also such speed does not provoke the initiation of the driving session – obviously, the NOx sensor is damaged;
  • if the contamination is below 500mg, possible scenarios – the NOx sensor is damaged, or – the performance of the NOx catalytic converter is very low (it is damaged).

In all scenarios – you can perform the last step.


3. Delete the contamination of the NOx catalytic converter. Description of the procedure here.

Attention: this procedure is dangerous because it can worsen the technical condition of the NOx catalytic converter. The NOx catalytic converter is not really cleaned from the sulfur, but directly the opposite – additionally contaminated. This procedure has to be done only in emergency cases and as rare as possible. This procedure is NOT a solution to the problem, but only a way how to make sure, that the cause of the problem is a NOx system.

After deleting the contamination of the NOx catalytic converter:

  • if Stratified charge is restored (at lest for several motor hours) – the NOx catalytic converter has lost its performance. Solution: replacing with a new one or installation of NOXEM;
  • a Stratified charge is restored for a relatively short moment or appears/disappears periodically (disappears longer than 5 .. 10 minutes) – the NOx sensor has a hidden defect. Solution: replacement of the sensor.


Note: if a Stratified charge is turned off for a long time due to problems of the components of the NOx system, for example the NOx sensor has any defect (regardless: hidden or the one, regarding which the error messages are recorded), or the NOx catalytic converter is contaminated with sulfur: during this time the NOx catalytic converter is not cleaned (regenerated/desulfated) and it loses the remaining performance relatively fast. So if you want to keep the NOx system in the OEM performance, it is critically important to maintain it (and all management of the engine) in such a technical order that the engine regularly uses a Stratified charge.