In this entry – one more example, how important it is to make a correct decision. In this case, the “pain” is relatively small – losses of only around EUR 500 and wasted time. But, if the problem is not solved immediately (additional investments of around EUR 400), the expenses can grow quite impressively shortly. 

The owner of the BMW with the N53 series engine approached me. He sent the diagnostics data. This time there was a “classic of the genre” – damaged NOx system. All possible error messages regarding the NOx sensor. The NOx sensor was not able to reach the Online mode. Without any illusions – the NOx catalytic converter was not in better shape. Mileage of the car: above 200.000; the age of the car: 10+ years. The car has driven with a damaged NOs sensor for a long time (without any illusions – for the last 8 years, since the manufacturer’s warranty has finished). 

I explained to the owner of the car that the NOx system can be repaired in two ways:

a. replacement of complete system (the sensor AND the catalytic converter), or:

b. installation of the emulator.

The emulator would allow saving on expenses, which would be replacing the expensive NOx catalytic converter. The car owner asked again – is the OEM NOx sensor really not the solution, to which he received a more detailed justification – links to the entries of my blog, which explain in detail all technical nuances.

Everything seemed clear and understandable. 

After a certain time, the car owner sent me a notice that he has repaired the vehicle, but something is not ok. The vibrations have not disappeared, fuel consumption is still increased.

My attention was drawn by the sentence: “From your attachment, I decided to replace the old sensor with the original new NOx sensor (+adaptation, etc…)”.

Note: the text in bold is originally from the author itself.

What, please? Why so?

The owner of the car asked me to evaluate the results of the repair. Here, the live data.

No error messages in the DME error message memory.

Data of the NOx sensor confirms that the sensor sends the data:

All data sent by the sensor are relatively correct; I don’t doubt that the sensor is really OEM and really new. 

Here, the injector learnbits:

Leranbits, marked with red, refers to a Stratified charge, and they should be colored. Uncolored learnbits mean that the DME is not using a Stratified charge!

For test – a view to the injectors data in Stratified charge:

Yes, there is a confirmation – DME hasn’t worked in Stratified charge/idle long enough even for one time, necessary to measure injectors (typically – a minute or two).

What could be the reasons for such behavior of the DME? There could be 3 reasons:

a. misfires. But in such case, (at least) the error message 3104 would be recorded;

b. feeble performance of CO catalytic converters in Stratified charge. But in such a case, there would be error messages 2A26 and 2A27 recorded; 

c. feeble performance of the NOx catalytic converter. 

In a very weak NOx catalytic converter, DME turns on the Stratified charge for a moment but turns it off very fast because it detects a very high content of the nitrites in the exhaust. For a longer period of time, DME makes sure regarding damage of the NOx catalytic converter and then records the error message 30E9, which stops the use of the Stratified charge forever. 

If DME does not use Stratified charge, it does not perform a range of important injector measurements – vibrations, misfires, and overloaded (and swiftly damaged) CO catalytic converter are guaranteed consequences. 

In this case, unfortunately, my verdict regarding a totally damaged NOx catalytic converter was true. Instead, the car owner’s decision to use an OEM NOx sensor is completely incorrect.

This repair had no sense. Even more – vibrations and the overload and damaging of the CO catalytic converters continue!

Sentence of this entry – sometimes it is worth following the instructions.