I am also owner of a sunny diesel since 2012. but story is no different from other owners rgd aftersale service. gud service before purchase only. my car average was 22/km in1st 3 months of delivery.
Later on it drop to 16.2 /km .no expertise could help and explain the reason. Manufacture r hardly concern for any after sale service contract we shall be happy of any guideline suggested by user Dr. Arun Ranchi.