In this entry – more about the service procedures, which refers exactly to the N43/N53 series engines.

If your car has NOXEM installed, you can not continue with reading, because the problems, described below, won’t affect you. But, if the vehicle has an OEM NOx sensor, several important nuances have to be taken in the account.


If any repair of the engine is performed, the readaptation of it has to be performed afterward. But in conjunction with the NOx catalytic converter (its condition and contamination with the sulfur) you have to take in the account: if the adaptations are deleted using INPA, the data of condition of the NOx catalytic converter (its status and the contamination level) are deleted, but, if deleting the adaptations using ISTA D/+, the status and contamination data of NOx catalytic converter usually are not deleted.


If the readaptation of the engine is performed via INPA, please, remember to always perform the desulfation (detailed description read here) of the NOx catalytic converter before readaptation. Why?

MSD80 calculates the contamination (and the performance) of the NOx catalytic converter, using 2 components:

a) amount of fuel, which has flown via it;

b) the amount of NOx, measured by the NOx sensor.

If the NOx catalytic converter has been cleaned recently, repeated deleting of its contamination (while performing the readaptation) won’t change anything. But, if the NOx catalytic converter is contaminated with sulfur but its status is deleted (because the readaptation is performed), trouble can appear. After the readaptation of the engine, DME will assume that the NOx catalytic converter has been cleaned (because its contamination data will be deleted), but the true performance of the catalytic converter will be poor (because it’s actually contaminated with sulfur). If the NOx catalytic converter is with a good initial performance, no need to worry – during the next cycle of desulfation, the catalytic converter will be cleaned. But, if the performance of the NOx catalytic converter is average (we have to understand, that we are talking about vehicles of age 7 .. 10 years – I doubt, that such old NOx catalytic converters will have a perfect performance unless it has been replaced), DME can detect an insufficient performance of the catalytic converter and record the error message 30E9. When the error message 30E9 is recorded, the data of contamination of the NOx catalytic converter are deleted, and the contamination is not calculated anymore – no desulfation is possible in the future. The NOx catalytic converter continues to contaminate – the situation gets only worse. Even if the same old catalytic converter is registered as “new”, during several hundreds of km DME will detect, that the performance of it is very low, and the error message 30E9 will be recorded repeatedly. With a damaged catalytic converter, the Stratified charge will not be allowed, many tests and adaptations of the injectors are not performed, during time – vibration, misfires, fuel trim error messages appear, etc.

This is a reason, why it is so important to perform the desulfation of the NOx catalytic converter before readaptation (if it’s performed, using INPA). When performing the desulfation, mandatory follow the process – is the request successful and the contamination level of the NOx catalytic converter drops or not.


In turn, if the readaptation is performed, using ISTA D/+, other problems are possible. If the error message 30EA was recorded previously: it is deleted not performing the desulfation, after readaptation of the engine the following situation is possible: Stratified charge is not restored, because DME (justly) considers, that the NOx catalytic converter is too contaminated.

If ISTA D/+ is used to readapt the engine, I suggest checking (mandatory), if the Stratified charge is restored after readaptation. For this purpose, identify the vehicle, perform its test, choose DME, press ‘Call up ECU functions”.

In subpart ”Diagnosis scan”, ”N43/N53: engine operating values” choose ”Display: operating mode”.

When driving evenly on a highway (with speed 70 .. 100 km/h), the engine should work in Stratified charge. If the engine uses Homogeneous mode, repeat the performance mode for several times with a time gap of 5 .. 10 min.

If the engine fails to use Stratified charge, check the status and data os the NOx sensor:

Two conditions have to be fulfilled:

a) the inscription ”all signals OK” should appear;

b) the NOx content should be different from 0 ppm.


If you see the inscription ”dew point detection expected”; ”no activity” or other and/or the content of NOx is 0 ppm – the NOx sensor is damaged!

If the NOx sensor indicates correct data, as already mentioned before – one of the reasons, why the Stratified charge is turned off, could be too large contamination of the NOx catalytic converter. To eliminate this problem, perform the desulfation session (detailed description read here).

After desulfation (during it make sure, that the level of the sulfur contamination drops) repeatedly check, if the engine has restored the Stratified charge. If the engine has restored the Stratified charge, perform several driving sessions of 5 .. 10 min + 5 .. 10 min with a speed of 70 .. 100 km/h and also idle (for DME to be able to perform the injector tests also in this mode).

Also in this situation – if the reason, why the engine is not using Stratified charge, will not be eliminated, the readaptation of the engine will not be successful. The NOx catalytic converter will continue to contaminate and will get damaged during the time.