The oil condition counter is a software algorithm in the engine control unit. It makes theoretical calculations based on operating conditions and measurements from various sensors including number and type of regenerations, ambient temperature, number of cold starts etc. etc. It cannot determine the actual condition of the oil, it is a guesstimate.
But if you let it run until it determines that (in its opinion) the oil; is degraded beyond its calculated cut off point, it will put the van in limp mode and shorty after progressively reduce its power and performance even further.
So resetting it prevents that from happening. It has no more effect on the physical condition of the vehicle than if you cancel a service required warning and reset it for a further 12 months, without having a physical service. The van is in exactly the same condition as it was beforehand, but the reminder has been cancelled and won't reappear until subsequent accumulated mileage or time dictates otherwise.
So you can reset the counter any time you like to prevent an eventual limp mode due to the oil counter, but don't forget to change the oil at the next required time or mileage to prevent risk of possible wear or damage to the engine.
I'm very much in the annual oil change camp, particularly if your van is a motorhome which probably travels relatively low mileages each year compared to a commercial vehicle, and spends a lot of time sitting around, either on sites or at home, rather than travelling sufficient distance to fully heat up the engine and evaporate or burn off contaminants in the oil every day. Some of those contaminants are the normal by-products of combustion that occur in any vehicle with an ICE engine, many of which are corrosive and/or acidic. But modern diesels can also suffer dilution of the oil by diesel, due to the regeneration process which, in the later Ducatos, can involve injecting diesel into the engine outside of the normal combustion cycle, to cause controlled overheating and raise the temperature of the exhaust gases sufficiently to burn soot deposits out of the particle filter. In those circumstances fuel can find its way into the sump diluting the oil.
I did read a document some time ago, which was a laboratory test of various long life oils intended for modern vehicles with emission reduction systems. It found that the protection offered by such relatively expensive oils was often comparable to, or less than that afforded by a cheaper traditional oil, after 24 months. But using the cheaper oil in the same vehicles would be even worse.
So I'm of the opinion that long life oils with extended mileage or time intervals and therefore less frequent service requirements are aimed by manufacturers mainly at attracting fleet buyers, who factor servicing and repair costs into their decisions when looking to purchase such vehicles. By lowering overall costs, the vehicle manufacturer hopes to attract sales to fleet buyers because their vehicle will hopefully cost less overall to run that a competitors' van.
With a 2 or 3 year warranty, and most fleet buyers disposing of the vehicles after 3 years or so, reliability and warranty claims are probably still within expected levels for the original purchaser. But as to the life of the vehicle subsequently, who knows, other than the certainty that there will be no comeback against the manufacturer at that age if any problems materialise.
I've also seen an engine workshop manual for the Iveco multijet engines jointly fitted to the Ducato and Iveco Daily etc. in which Iveco state that any vehicle travelling less than 7,500 miles a year should have annual oil changes rather than the headline 24 month service, and that any engine not started and driven for 3 months or more should have an oil change before being started. Fiat are rather less informative, only alluding to 12 month oil changes for vehicles driven mainly in towns, whereas the manufacturer of my car also stipulates the same reduced change frequency for use in adverse conditions including cold climates, deserts, mountainous areas, predominantly short journeys, towing a trailer etc.
So that's what I have based my annual oil change decision on, and at less than £60 for Fuchs oil as used by my local Iveco and Fiat Pro dealer when my van was in warranty, plus a decent filter (MANN) and an hour or so of my time, its hardly expensive.
I would guess that a 13 year old Citroen petrol car didn't have a modern engine with relatively tighter tolerances, and certainly didn't have a diesel particle filter regeneration system. Even so, I've seen the difference between the inside of engines of all types subject to regular oil changes using good quality oils, which often appear as clean as a whistle internally, and others
I'm also far less fussy about the type of oil I put in my wife's 15 year old Hyundai than the van or my nearly new Volvo, but then the Hyundai's engine is based on much older technology and a pretty basic design! I still change the oil and filter annually though, even though the intervening mileage is usually less than 3000 miles.
