OEM NOx sensor vs NOXEM

In the situation, when the mileage of the vehicle is relatively small (below 120’000 .. 150’000 km) and the error messages regarding performance of NOx sensor are stored, but the error message 30E9 (regarding aging of NOx catalytic converter) is not stored, we note, that the owner of the vehicle has two options:

a) install new OEM NOx sensor;

b) install NOXEM.


If there are error messages regarding the performance of NOx sensor and also the error message 30E9 is stored, not depending on the mileage, the owner of the vehicle has following options:

a) install new OEM NOx sensor and new OEM NOx catalytic converter;

b) install NOXEM (in this case no replacement of NOx catalytic converter is required).


To make it easier for you to make a decision, which solution to choose, check the advantages/disadvantages of each option.


OEM NOx sensor


a) allows to keep the construction of the vehicle exactly as is was intended by the manufacturer;

b) ensures max low level of NOx in the exhaust – saves the environment.



a) life-cycle of the sensor averagely is quite short – around 50’000 km; unfortunately, also specific hidden defects are very common – they can appear even before reaching the average lifetime of the sensor;

b) if the NOx catalytic converter is with decreased performance, even perfectly performing NOx sensor will not help and the error message 30E9 will be recorded – it can happen every moment*;

c) even with the relatively good performance of NOx catalytic converter, if the mileage (averagely) is above 50’000 km, the desulphation and regeneration of NOx catalytic converter are quite often – it increases fuel consumption;

d) even in case of relatively good NOx catalytic converter performance, desulphation of it is required after each 1000 .. 1500 km (driving with speed at least 110km/h, at least 20 ..30min). If these sessions are not performed in time, MSD records the error message 30EA, turns off Stratified charge and the engine has typical problems – increased fuel consumption, vibration, misfire etc.


* if the error message 30E9 is recorded, the only solution to restore normal performance, using OEM NOx sensor: replacement of NOx catalytic converter (as mentioned above).


If the vehicle has experienced problems with NOx sensor for a long while (5’000 km and more) and it has not been replacing immediately, we recommend to install NOXEM. While the NOx sensor was damaged, the NOx catalytic converter hasn’t had necessary desulphation and regeneration sessions, and its performance is significantly lowered. The possibility, that after replacing the NOx sensor, MSD management system will detect decreased NOx catalytic converter performance and will record error message 30E9, is very high, and it all makes replaced OEM NOx sensor useless.


The average lifetime of NOx catalytic converter is around 150’000 km. Around 10 .. 15% of all inspected vehicles, already after 100’000 km had damaged NOx catalytic converter. Of course, there are also vehicles, which NOx catalytic converter is performing well also after 200’000 km, but this is a very small amount (one from several hundred). If the mileage of the vehicle is close to 150’000 km, we recommend to install NOXEM – if you choose to install OEM NOx sensor, MSD can detect insufficient performance of NOx catalytic converter and record the error message 30E9 in every moment, and it makes the new OEM NOx sensor useless: Stratified charge will be prohibited, and the engine will suffer all problems described here.

If you are driving mostly long distances – long drives on the highway, the NOx catalytic converter will maintain the performance abilities for a longer time. If you are driving mostly short distances with low average speed (city mode) – unfortunately, this is a bad mode for NOx catalytic converter.




a) ensures correct performance of the engine independently of the performance of the expensive NOx catalytic converter (it can be even disassembled);

b) ensures additional fuel economy (desulphation and regeneration of NOx catalytic converter are performed as rare as possible);

c) independently from real performance of NOx catalytic converter (it can be even disassembled or replaced with resonator), desulphation sessions are necessary after each 6000 .. 7000 km, additionally it is possible to not perform them at all (for example, if the current region has no highways with speed limit above 110 km/h) – after each 7000 .. 8000 km the coding of new NOx catalytic converter, using computer, has to be performed (it takes about 5 minutes);

d) NOXEM is much more robust, it’s resource – much longer. In case of the normally performing engine (without increased oil consumption), NOXEM will serve 300’000 km or even longer.



a) in several performance modes the amount of NOx will exceed standards, restricted in EURO 4.

Here we have to add, that if the engine performs correctly (Stratified charge mode), it has the much lower amount of CO and CH in the exhaust – that, in turn, is a contribution to the environment. More about this read in FAQ (Q/A No:5)