From ww.honestjohn.co.uk - he has a column in Daily Telegraph so it in intended for UK Readers but most is still relevant.
"67. WARRANTY SERVICING: What happens to my new car warranty if I have my car services outside the franchised dealer chain?
The EC has Directed that a manufacturer warranty cannot be affected by a car being serviced outside the franchised dealer chain.
But it must be serviced to the manufacturer stipulated schedule, using the specified fluids and parts. An independent garage cannot, for example, use its bulk oil and an aftermarket oil filter if these differ from the manufacturer specification.
In the UK, the SMMT has secured agreement that this also covers the second year and third year of the warranty, even if these are described as "conditional dealer warranties".
Further warranty, such as KIA's 5 year to 7 year warranty and Hyundai's 5 year warranty, depend on franchise dealer servicing from the start.
As does Mercedes Benz 30 year Mobilo cover on some parts of the car.
There are three other potential pitfallls for owners who service outside the franchises during the warranty period.
An ordinary garage may not have the electronic equipment or software to carry out electronic parts of the service via the OBDII port, and may not even be able to reset the service indicator.
An ordinary garage will not be aware of 'Technical Service Bulletins' issued by manufacturers to franchised dealers to carry out updates on the car during the course of a service.
And a manufacturer will not be as sympathetic towards providing 'goodwill' once a car is out of warranty if it has not been serviced by its franchised dealers.
Finally, independent servicing greatly reduces the part-exchange value of a car for the first 5 years or so. Many franchised dealers (particularly Audi) dealers will not buy in stock that has not been Audi maintained throughout its life.