Aging of the Lambda probe

If the Lambda probe is damaged or clogged so much, that its signal is incorrect – most probably, there will be error messages recorded regarding this problem.

In this entry – about one symptom which allows noticing aging of the Lambda probes before any error message is recorded.
What indicates the aging of the Lambda probe? Increased PWM of its heating!


Here, an example:

and Nernst resistance (chemical efficiency) of the probe:

As we see, the Nernst resistance is correct (correct values: 0/256 Ohm), but the PWM of the probe heating, to reach this Nernst value for 20% (at least) higher than for the second control probe.

What does such increased PWM indicate? Obviously, the probe with correct PWM can not reach the necessary chemical efficiency, so DME has increased its heating. It is terrible news – the Lambda probe will not be able to endure such thermic overload. So it is recommended to purchase a new Lambda probe on time and get ready to replace it.

Note: DME measures Nernst resistance (chemical efficiency) of each probe approximately once a second. Via I (current) source, the signal of the signal output is connected to the voltage of +5.0V, and the changes of U (voltage) is measured. Optimal values of Nernst resistance: 80 .. 300 Ohm (according to the Datasheet of probes). Step of the values, displayed by INPA, is 256 Ohm. Accordingly, correct values of the INPA menu: 0/256 Ohm (512 Ohm are allowed for a short time). PWM of heating is managed according to the management map (taking into account the simulated temperature of the exhaust gases and exhaust rate/pressure), which is supplemented by the adaptation Offset, taking into account the differences of measured Nernsts resistance against the ideal value.