I have been having exactly the same problem with my T reg 2.1 diesel Xantia... Previously when I drove a Peugeot, I would get a very similar effect from the warning lights when the oil was low. I have topped up the level of oil, but the lights keep flicking on more regularly. I am going to top up the water level today and add some antifreeze as I am not sure it has any in the system (when I work out how, as I don't have my Haynes manual to hand) Would be really interested to find out how to solve this issue... All the gauges are reading normal levels, and the car drives fine... it's not overheating. I wondered whether the sensor was faulty...