Problems and performance check of NOx sensor

The NOx sensor is comparatively quite expensive spare part, it’s price is around 450 .. 500 EUR, but work-life: very limited.


How to evaluate the performance of NOx sensor?

1. The error message memory of MSD80 contains error messages regarding NOx sensor (the list of error messages you will find at the end of this post). In this case, unfortunately, the sensor has to be replaced. No cases, when the error messages regarding NOx sensor are recorder without correct reason, have been observed, just few exceptions:

  • 30DE, which can be recorded, when the exhaust is mechanically damaged (significant inflow of air); incorrect operation of Lambda probes (problems with wide-band or control probes); incorrect injector’s adaptations (leaking injectors, misfires, etc.);
  • 30D6 in situation, if Lambda values, measured by wide-band probes, incorrectly fluctuates (problems with probes, leaking injectors, air inflow);
  • 2EAE in situation, when the NOx sensor don’t receives +12V/Ground power supply voltage or there is a problem with data communication (no contact in connector and/or damaged wireset). Detailed info: read here.

2. There are no error messages in MSD80 memory, but, possibly, the error message 30EA is present or – the engine has unavoidable problems with Rough run, misfire, bank and /or cylinders individual adaptations. Such case requires specific check-up of NOx sensor – some specific abnormalities can exist also without recording in the MSD80 error message memory.

Note: 30DE, 30D6 can be recorded after NOx sensor’s replacement, if new sensor is not encoded. Please, proceed encoding of new NOx sensor after replacement as described here.


Conditions for Online (data transmit) mode of NOx emulator:

a) engine warmed up to work temperature

b) exhaust temperature at least 220 oC

c) driving with the speed at least 20 km/h

d) conditions a..c are kept at least within two minutes


Detailed description

Heat up the engine to work temperature. Check your car’s engine temperature: ../F5/F2/F6.

After few minutes of driving temperature should be 90 .. 105 oC.


Open the manu of NOx sensor / exhaust gas temperature, using INPA:

  • ../F5/Shift+F2, if the INPA loader 1.01 is used;
  • ../F5/Shift+F2/F1, if the INPA loader 2.023 is used.

Heat up the exhaust system till (at least) 220 oC (bar No.1 in the image).

Note: conditions (engine and exhaust system temperature readings) mentioned above are compulsory requirements for normal operation of NOx sensor.


Drive your car with speed at least 20 km/h.

During two minutes after necessary exhaust system temperature and driving speed has been reached, the content of NOx has to become different from 0 ppm (bar No. 2 in the image) – it means, that the NOx sensor starts to send data to MSD80.

If the content of NOx still is 0 ppm or/and becomes 0 ppm, the NOx sensor is damaged (the sensor element has aged) and it (the sensor) has to be replaced. If the sensor starts to send data periodically (not continuously – during all driving session), MSD80 will have no error messages recorded in it’s memory, in the same time – Stratified charge and Homogeneous lean mode, desulfation and regeneration sessions of NOx catalytic converter will be disturbed. As a result, the error message 30EA will be recorded in the MSD80 memory, even if the driving speed regularly will be above 110 km/h, and also forced desulfation sessions will not be possible (won’t be successful).

If the sensor sends data stable/continuously (the content of NOx is different from 0 ppm all the time), the offset of sensor in Overrun mode has to be evaluated: see bar No.3 (in the image above). If the bar No. 3 is highly above 5 ppm (critical border: 15 ppm), the sensor has been aged (the chemical element is clogged) and it has to be replaced. Using such sensor (with increased Offset value) will lead to problems in near future ( the error message 30E9 regarding aging of NOx catalytic converter can be recorded prematurely; as soon as MSD80 will confirm the increased value, it will switch off the Stratified charge and Homogeneous lean mode, and the engine will encounter all problems, which are described here.

If the parameters named before are within the normal range, the Lambda measured by sensor have to be evaluated (bar No.4 in the image above). This Lambda has to correspond with average value of Lambda measured by both wide-band probes of engine (exception: overrun mode, see below). If the Lambda, measured by NOx sensor at Homogeneous mode (Lambda 1,00), has significant differences (more than +0,02 .. 0,03) from  measurements of engine’s wide-band Lambda probes (Lambda is increased) – possible air inflow in exhaust system has to be eliminated, or, if it’s not detected (or – Lambda measured by NOx sensor is significantly lower than measured by wide-band probes) – the NOx sensor has to be replaced. Of course, in case of huge mismatches MSD80 will “notice” them and records the error message 30DE, but – this mismatch has to be really huge. If this defect is not rocognized in time, more problems will appear – error messages regarding NOx catalytic converter, misfire, incorrect adaptations.

Lambda evaluation in the overrun mode. Drive your car at 90 .. 110km/h in 5 .. 6th gear (use manual mode for automatic gearbox) and release accelerator pedal. After few seconds Lambda value (bar No.4) should reach 20 .. 32 (at the same time wide-band probes will report Lambda 16,0). If the value is lowered or is reached after a long time (more than 5 seconds), the sensor is clogged and should be replaced.


Error messages, which apply to NOx sensor:

2AEC Nitrogen Oxide Sensor Self Diagnostics

2AF0; 2B05 nitric oxide sensor, heating

2AF2; 2B06; 2B09 nitric oxide sensor, Lambda linear

2AF4; 2B07; 2B0A NOx sensor, electrical

2AF6; 2AFB; 2B0B nitric oxide sensor, Lambda binary

2AF9 nox sensor, nox signal: coast mode check

2EAE NOx sensor message missing (timeout)

30D6 nitric oxide sensor, plausibility

30D8 NOx sensor, Sensor damaged

30DA NOx sensor, heating time

30DC nitric oxide sensor, heating

30DE NOx sensor – Lambdaprobe before catalyst, Korrelation

30E0 NOx sensor, Offset

30E2 nitric oxide sensor, thrust test

30E4 nitric oxide sensor, aging

30E6 nitric oxide sensor, dynamics


Related entries:

Encoding of new NOx sensor

Replacement of NOx sensor

NOx sensors. OEM codes

Error messages. Intro

Advanced features of MSD80