I know this topic has been done to death, but even using the search I can't find the answer to my question. Which is simply is this message driven by arithmetic (i.e. you've started the car x times to do y short journeys so on it goes) or is it in some way smart and actually analyses stuff before activating the message. You've probably guessed by now that I have got the message despite doing an oil change and a service reset only a couple of months ago and maybe 1500 miles since then (but lots of short journeys). I don't mind changing the oil again but is it actually necessary. It certainly doesn't use the date as the 12 month service is due in November. Geoff

It’s purely a calculation based on various measurements in the ECUs. It in no way physically tests the oil quality.

The main issue is if there have been failed regens of the DPF as it will assume oil dilution. But also short journeys will count towards this short interval and also high speed motorway driving - which surprised me as I thought that was the best thing for the engine.

From what I have read from people who had had actual oil analysis carried out, the oil was in a far better state than the service required message suggested.