In this entry, I will mention root causes, which have to be blamed in premature damages of the NOx sensor and also different ways to prolong the lifespan of the NOx sensor.

This entry applies both to the OEM sensor and NOXEM. NOXEM also uses the oxygen probe to measure the parameters of the exhaust. Yes, the probe, used in NOXEM, is more sturdy and more long-living than the probe of the OEM sensor, but it also has its strength limits.


What damages the sensor and how to avoid it:

1. Water. How does the water get in the exhaust? In the exhaust, the air moisture is condensed. The water is also a sideproduct of the work of the CO catalytic converters. How to prolong the lifespan of the sensor? Regularly drive for longer distances for the exhaust to get warm-up thoroughly and the excess water is discharged. Short drives – the fastest way how to damage the NOx sensor.

2. Fuel. If any of the injectors is leaking, unburned fuel gets in the exhaust and gets ignited at some moment. If any of the cylinders are misfiring, also the oxygen gets in the exhaust. Fuel and oxygen – a perfect combination for burning or even exploding. How to prolong the lifespan of the sensor? If you observe a permanent vibration (typically) during cold start and after it, shivering of the engine on the go, if EML (Check engine) lights up – solve the problems immediately! Leaking injectors and misfiring cylinders will damage the NOx sensor and also can damage other Lambda probes and CO catalytic converters! The longer you will postpone the repair, the more expensive it will get!

3. Mechanical damage. If any piece of rock or any other foreign body hits the probe or the exhaust, it can damage the NOx sensor. The measuring element of the sensor is a very thin and fragile ceramic plate – blow to the body of the sensor is deadly for it. It is very hard to avoid such damages, if only – drive very carefully on the gravel road and across the larger (higher) barriers.

4. Different additives for “improving” the performance of the engine. Anything, that is intended to clean cylinders and valves, improve the compression, reducing the exhaust gasses, increase the power, etc. All these additives can (and very often it happens) permanently damages Lambda probes, CO catalytic converters and also can be a cause of leaking of the injectors. Solution – not under any circumstances use any of “improving” additives!

5. Increased oil consumption. If the engine has increased oil consumption, burned oil settles in the exhaust – in CO catalytic converters and Lambda probes – and damages these elements. Solution? Avert the reason for oil consumption. For the engines with a normal mileage reason for the increased oil consumption – defects of the crankcase ventilation.

6. Other reasons for incorrect fuel mixture. If the fuel mixture is enriched, the fuel gets in the exhaust, burns there and the soot is formed. The sooth “sticks” the probe of the NOx sensor – it can not feel the content of the exhaust gasses anymore. Suggestion – regularly check the N43/N53 series engines with a knowledgeable specialist (or perform the Online diagnostics with Bimmerprofs) to make sure, that all systems of the engine work as they are supposed to. Incorrect fuel mixture damages also the CO catalytic converters – all problems of the engine should be repaired as soon as possible.

7. Thermal shock. This can happen if you drive into a deeper puddle or snow-drift. Near the NOx sensor, the exhaust is hundreds of oC hot (or even more when driving aggressively, or if the DME is desulphating the NOx catalytic converter). If water reaches the exhaust, its temperature drops sharply. Rapid temperature changes also can damage the NOx sensor.