My 2010 Nissan Micra has done 15,000 miles and had three services with a main dealer. Two weeks ago I took the car to an independent garage for its fourth service, but when I got home the oil warning light came one. The sensor has been changed to no effect, the sump removed and strainer cleaned replaced and refilled with the correct oil, The garage has also fitted a new filter, but the problem still remains. There is no sign of an oil leak. I believe the pump is chain driven. Do you have any advice?