* E6 Euro 4 specification - low SAPS for vehicles with PDF (see below)
New low SAPS (Sulphated Ash, Phosphorous, Sulphur)
This oil is a recent introduction for diesel engines fitted with a DPF (Diesel particulate filter). This is effectively a filter unit in the exhaust that takes out the microscopic soot particles. If you don't use a proper low SAPS oil, then the additives can block the filter with ash, which is a bit like putting a potato up your exhaust! New filters are pricey - £1500 isn't unusual.
* C1 Low SAPS (0.5% ash) fuel efficient
* C2 Mid SAPS (0.8% ash) fuel efficient, performance
* C3 Mid SAPS (0.8% ash)
Many OEM are now using their own specifications to capture this spec. eg. Mercedes 229.31/51, BMW Longlife 04, VW 507 00 etc.