I recently had my car repaired and got brake pads replaced along with a major tune up which included changing spark plugs, filters, oil etc. Now my car turns off suddenly in the middle of the road. It also happens sometimes when I have to stop at the traffic light. I noticed that it is more often when there is less than one third gas in the tank. The mechanic says that everything seems fine and he cannot help because it happens once a while randomly. Please let me know what needs to be done and is the problem due to some defective part he might have used during tune-up. Is fuel pump at fault?