The Harrier mileage is 14.6 to 16.35 kmpl. The Manual Diesel variant has a mileage of 16.35 kmpl. The Automatic Diesel variant has a mileage of 14.6 kmpl.
For this, we'd suggest you please visit the nearest authorized service centre of Tata as they would be able to assist you. Follow the link and select your city accordingly for service centers.