Re: Change engine oil warning on 159 1.9jTDM
I actually work in this area and I'd say it's very unlikely that there's actually an oil quality sensor in the vehicle, I think Mercedes have just developed one and they're generally the first to shell out on the R&D for this sort of thing! Could be wrong though!
The way we do it is to just predict how much soot and oil is going into the oil based on engine load, speed, oil temperature, DPF regens etc., there's nothing actually measuring the quality of your oil.
The light is triggered by either maximum soot in oil limit, maximum fuel in oil limit, maximum distance since last oil change or maximum time since last oil change, whichever is reached first.
Since there is nothing actually measuring the oil, if you change it and don't reset the light it will stay on (unless the change tops up the oil and you have a level sensor which detects this extra oil, bringing down the percentage soot or fuel in the oil, but then it will trigger sooner than you expect next time), and likewise if you reset the light and don't change the oil then you risk driving around with crap oil.
If you get the change oil light then get the oil changed AND reset the light at the same time. That way the light calculations and the oil are in sync.
Generally stop start drivers will trigger on fuel or time and long distance high speed drivers will trigger on soot or distance.