The auto transmission warning light in my 2003 Renault Scenic has come on a few times, and when it does I lose power in the car. Once I stopped for a few minutes the car was ok to drive again. This has happened twice and on the third occasion I heard a loud "clunk". I stopped the car and had my mechanic check it out, but he could not find any faults showing in the computer and none in the computer memory! He is at a loss as to why the light is coming on, and has suggested that I sell it. I feel very unsafe driving this car.
There is a fault associated with the auto transmission and the warning light is indicating as such when it comes on. The fact that loses power suggests that it is going into limp home mode, which is designed to give you enough power to drive on to a mechanic or dealer. That it isn't on when the mechanic checks it says that it is an intermittent fault, which can be hard to trace. I would take the car to a Renault specialist and have them check it.