The odometer of my everyday car indicates 600.000km. I believe it’s sufficient mileage to have my own opinion from my own experience.
I purchased the car with a mileage of 100.000+km. Checking the BMW AIR system data, I found out that the NOx sensor was replaced two times during the first two years. It happened around 25.000 km and 50.000km. I assume that the problems were noticed during oil changes. Accordingly, the true serving time of the NOx sensor is not known, but it is clear that it was less than 20 .. 25.000km. I assume that significantly less, because – if the error message regarding this sensor would be recorded only several times, I doubt such an active action would follow (typical first reaction: delete the error messages, observe the situation). After installing the third sensor, installation records in the AIR system stopped. As can be understood, the standard warranty time (2 years) was over, and the car owner chose to perform the service in some cheaper service.
When I bought the car, the situation was following:
Already by the milage around 100’000km, the error message 30E9 (insufficient performance of the NOx catalytic converters) was recorded, the engine (logically) was not using Stratified charge;
Already by the mileage around 70 .. 80.000km in History memory, all possible error messages regarding NOx sensor were recorded. Obviously, the third sensor also hasn’t lasted for a long time, and at least No.4 was already installed.
In addition, the existing sensor also had problems. The proof of that was the error messages 2AF2; 2AF4; 2AF6, which appeared sometimes. The sensor only sometimes reached the Online mode and started to send the data.
The mechanical efficiency of cylinder No.5 was incorrect – reduced. The replacement of the injectors and readaptation of the engine did not help. DME was not using Stratified charge; was not performing the injector measurements in this mode. As a result – permanent vibration in idle did not disappear (it was present all the time) when driving misfires could be felt. Needless to say – replacing the spark plugs and ignition coils did not make the situation better.
The error message regarding the reduced performance of the CO catalytic converters of the 2-nd bank appeared regularly.
I installed the NOx emulator, re-adapted the engine. Further listing starts from this moment.
Performance of the cylinders evened out, the problem with cylinder No.5 disappeared. Also, the misfires in cylinder No.5 disappeared.
Also, the error message regarding the CO catalytic converter of the 2-nd bank disappeared. The error messages regarding CO catalytic converters repeatedly started to appear after a mileage of 400.000km. By the mileage of 450.000km, new OEM catalytic converters were installed. During the last 150.000km, the error messages regarding the performance of the CO catalytic converters haven’t appeared.
The problems with starting a cold engine in temperatures -15 .. -20oC disappeared (the emulator was installed in winter, I had a chance to evaluate the progress several days before and after installing the emulator).
The engine subjectively became much more responsive, “lighter.” The fuel consumption was reduced by around 20%.
With a mileage of 250.000km, the engine was completely rebuilt to the most powerful version. The software of the iX model was “sewn-in” in the DME because it turned out to be the most aggressive in the modes of max required torque.
I believe many of you are interested. What would I say regarding the longevity of the emulator? Would I say that it serves lifelong? No, it is not so!
In the emulator, the original Bosch LSU 4.9 Lambda is used – the actual product of the manufacturer, tested for several tenths of years. Robust, long-lasting, high quality. But – it also has its endurance limitations. As I have already mentioned in the blog, the probe can be damaged by water, fuel, contamination (for example, oil), fuel additives, mechanical shock.
So – I made several “fails” to exactly identify which injector is leaking. I kept to the strategy: replace only the injector, which was working incorrectly. The idea of this approach is simple:
Find out the true lifespan of the injectors;
Find out – the injectors start to leak due to wear or due to other obstacles (which don’t correlate with the wear).
With the dealer’s approach: install new injectors, if the release of any is different from the newest one (the 11-th) and – replace all injectors in the problematic bank – the NOx sensor would suffer less. Accordingly – it would serve longer.
The first probe of the NOx emulator was destroyed after 210.000km. I was driving with an average speed of around 80km/h, 20 .. 30% required torque; I released the accelerator pedal to reduce the speed evenly. Several seconds later, I felt a strong blow from the bottom of the car; in KOMBI the EML symbol (“Check engine”) lighted up. I decided that some larger stone has hit the car’s floor (possibly – the exhaust). The inspection of the error messages showed that not taking into account that DME was working on Mode 3 (Stratified charge), one of the wideband probes of the bank has reported a rich (!) mixture. The NOx sensor was online, but in all modes (including Overrun), Lambda linear was 1.00; Lambda binary: around 510mV. The visual inspection of the exhaust did not indicate any signs of damage from the stone. No slightest doubt has left – some injector (one of the 3 of the current bank) has stuck in the open position, the air, which has got in the exhaust in Overrun mode, together with the fuel created a flammable mixture, which exploded. The explosion destroyed the probe of the NOx sensor. When the probe was dismantled, inside it, “something” was shaking – the ceramic plate was broken.
The same injector created problems several more times (till I got indisputable evidence that exactly it was the culprit). These problems were the cause of the replacement of one of the wideband probes. The probe was strongly contaminated; in the Homogeneous fuel mixture, it showed Lambda>16.0.
The second probe of the NOx emulator managed to survive the “attractions” previously and served for 160.000km. In this entry, I describe the problem as if new injectors, which were behaving very strangely. This probe had to endure a lot. Both leaking of the injector in idle and sticking in the open position. In the second case, from the car’s exhaust pipe, a cloud of pungent smoke was coming out. I had purchased 6 (!) such low-quality (probably, used ones) injectors. This probe “survived” 5 of them. This probe’s endurance was done when the 5th injector “managed” the situation with the pungent smoke from the exhaust. The probe started to indicate increased Lambda. It should be added that already from the fateful crash, the probe indicated increasing problems. After each smoke cloud due to injector “performance,” Lambda in Overrun mode was getting lower. From the initial 25+, it has dropped to 5 .. 6. Yes, at the moment, when the injector was not making, the probe started to recover slowly, but the defects of the injectors, obviously, were too often and too impressive.
The third probe of the NOx emulator served till the mark of 600.000km when it was “caught” reporting increased Lambda during the first minutes after warming it up. There were no error messages in the DME error message memory, but – live data indicated that the probe is poisoned. Yes, the reason was clear. One of the defective injectors started to stick in an open position more and more often, another injector, which has served 400.000+km, also started to “behave”. According to the symptoms, the problem of the probe was actually already for some time. It is possible that so – without error messages, the probe would continue to work for a long time. The leaking injectors were replaced, with a possibility of 50/50 the probe would even “recure”. But – the car should be in technically good order, and the probe was replaced immediately.
So – three probes together have survived almost for 500.000km. Additionally, I already mentioned that I deliberately did not replace “old” injectors (for example, my car still has one injector of the 07th release, which has served 600.000km).
Conclusions regarding probes used in the NOx sensors/emulators:
The original sensors on my car have served much less than 20 .. 25.000km. In addition, the car had new injectors, minimal oil consumption, a perfect driving profile (long drives in DE). The NOx catalytic converter, not taking into account the replacement of 4 pieces of the NOx sensors, has served for only around 100.000km;
In my case, Bosch LSU probes serve for around 150.000, taking into account that I deliberately allow the leaking of the injectors (till the exact culprit is identified); I don’t replace the injectors after exact mileage.
I do not dispute that the Bosch probes can also be destroyed much faster. People drive 5 .. 8.000km during the year with these engines and use them for short drives (one driving session just 3 .. 5 km). Of course, in such conditions, the water is collected in the exhaust. DME cannot measure the injectors – an incorrect fuel mixture is created, leftovers of it get to the exhaust. The fuel vapors increasingly accumulate in the exhaust (the cause of it could also be enriched fuel mixture for swifter warm-up of the CO catalytic converters). Unfortunately, in such conditions, even the most durable Lambda probes can’t survive!

In the picture: Bosch LSU 4.9 Lambda probe after 150.000km. As you see, there are both “confirmations” for enriched fuel mixture (black residues) and lean fuel mixture (light grey residues).
In conclusion: in none of the cases (also checking the data of other users, in which I see the resource of 100 .. 200.000km), I haven’t noticed such aging (slowing of the performance) of Bosch probes significantly impact their performance. Son – if the probe is not mechanically damaged or poisoned, it can serve 200 .. 300.000 km without problems.
Bosch suggests replacing the probes after each 100.000km. LSU 4.9 is not the most expensive component in these BMWs, I believe – even the economic user of this engine can afford it.
The most important – perform the express diagnostics of this engine regularly and don’t ignore the vibration, shivering, smoke, and “Check engine” symbol!