I own a 2007 Citroen C4 Picasso with the 1.6HDi engine (about 110bhp I think) with the DPF. However it seems that it is essential for these engines to be run with C2 grade engine oil (low sulphur and ash content). Unfortunately, prior to me purchasing my car second hand with 13,000 miles on the clock, the car had been serviced by a Citroen dealer with Shell Helix F, which is not C2 grade. Two years and a service with the correct oil later (at 25,000 miles on the clock), the turbo has failed, which will cost a whopping £2,500 to repair at my local Citroen garage. A quick Google on this issue suggests this is very common on this engine, which is fitted to Citroen, Peugeots, Fords, Volvos and, until last year, MINI Cooper Ds. I contacted four well-known turbo specialists in the UK. All of them commented to the effect of "there is a problem with the 1.6HDi engine in these cars", and one refused to sell or repair the turbo for this engine altogether as it would "probably fail again soon after replacement". My local Citroen garage has request support from Citroen for the replacement, but here is the catch: Citroen has requested some extensive diagnostics work (£500), which I have to pay before they will consider the claim, which of course they have no obligation to support. I wonder if this is a deliberate effort to prevent either out-of-warranty replacement costs *or* the rejection of claims for the same appearing in their records? As it stands it seems I have little option but to get the car repaired at an independent garage, for about £1,500, and then move the vehicle on as soon as possible. It seems far from ideal.