my peugeot 406 shows stop on dash board.Temp gauge rises and falls while driving.

l have the stop sign come up on my 405 mi16 however it goes off after a few mins some kind of electric fault with sensor reading l guess . Have been told not to worry even though in the handbook it says take straight to a main dealer. With the temp gauge as long as it comes back down when the fan kicks in the no probs its a peugeot thing as all the pugs l have had done the same thing. hope this helps

The low cost trial solution is to replace the thermostat.
It may be too old & too slow in opening & closing, letting the water get too hot, then opening late.
Too hot makes the STOP light come on.
Also, how long has it been since u replaced the coolant? That old mixture could be approaching the boiling point too easily. Try changing that too. It is not an expensive trial solution either.

3 DAYS LATER:
l just thought of something else: The water temperature sensor for the 205 Gti, the 306, & the 405 r all found in the water thermostat housing. Look at ur 406, where the upper radiator hose connects to the engine block. You should/might see an electric sensor with two wires screwed into the aluminium housing. This sensor is removeable with a spanner (you will loose 1 litre coolant) & can also be replaced. cost?? This might be a faulty sensor, giving readings intermittantly to the dashboard guage. & ur temperature is really OK, always 90 C or thereabouts?

You can do this job yourself in the driveway. If l am wrong, u have spent 5 to 10 pounds, & one hour. If u coolant is relatively new, then save ur coolant & reuse it.