This time – a very simple case. But I am sure that it will be useful for someone who just started to learn diagnostics.
M54 series engine with MS45 management. During the preventive examination, an unexpected error message was noticed:
Obviously, something is wrong with the control probe of the 1st bank. Is fuel mixture to blame? Or the probe itself? The error message is regarding the control or connection of the probe. DME has detected that the load has disappeared – there is a rupture in the circuit of the heating element of the probe.
Pay attention to the marked parameter: it’s Nernst resistance (“internal” resistance of the probe) – the chemical efficiency of the probe.
As we see, the Nernst resistance is very large (around 65K Ohm), which means – the chemical efficiency of the probe is 0. The probe is not working; one of the possible reasons – it is not warmed up. At the same time, the voltage supplied to the heating element: is 99.61% of the onboard voltage. Obviously, this time, DME is not wrong – the problem is exactly with the warming up of the probe.
Let’s check live data.
We see that all probes are warmed up (first two lines in the image above). MS45 uses narrowband probes both before and after catalytic converters. All probes have 12V heating elements, and the onboard voltage is supplied to them directly without stabilization. The indicated 99.61% means that 99.61% of the time, the onboard voltage is supplied to the heating of the probes, but 0.39% of the time is used to check the connection of the heating element of the probe (and also the “health” of DME output too).
The main probes of both banks indicated a voltage 0.1/0.7V (this voltage changes with a frequency of approximately 1Hz), which means – the fuel mixture in both banks is Stoichiometric. It means – correct, with Lambda 1.00.
The voltage of the control probe of the second bank is stable, around 0.7V, which means – the catalytic converter is in working order; it burns oxygen.
Instead, the indication of the Lambda probe of the 1st bank is 0.42V, and it does not change. 0.42V means – the probe is actually inactive. Damaged. Turned off. With 0 chemical efficiency. 0.42V to the DME input is supplied directly from the internal Voltage source exactly for the needs of self-diagnostics. If we see such voltage, there is no doubt – the probe is not performing its duty.
Unfortunately, MS45 with INPA does not show data of the Nernst resistance of the probes, but all possible symptoms say – in this case, the heating element of the probe is damaged, and the only solution is to replace the probe.
