Just recently, the heating-up lamp has been coming on in my Renault Scenic 1.9 Diesel while I'm driving. It usually happens on the motorway, doing about 65-70mph, going up a slight incline. I can feel a bit of deceleration and when I look, the lamp has come on. It goes off again once the road levels off. Come on, all you petrol-heads, what's going on here?
Do you mean the glow plug light, if so this should not be happening, not good for the plug lights. Check in the handbook if it is used for another warning. Do not know what would put it on under the conditions you discribe.
Silly Idea, are the keys on a large bunch, they could be pulling the key onto the glow plug position as you go up hill?.