Engine blower, once started, won't turn off

[Subsonic]

Hi all... i have one big problem with my 406 (1997, 1.8 16v petrol) which is still unsolved.

The engine blower start to work at maximum speed once when car engine temp reaches 70 degrees (until 70 everything is OK). And when the engine temp hits 70 degrees, blowers start to work at max and "STOP" on dashboard turn on. And they won't set to slower speed. It is very annoying and im sure it's not good for the engine. When i turn off the car, and the engine temperature goes under 70, next time when i start it everything is ok until it reaches 70...

I've tried to change resistor box (under the passenger footwell ) and i have same thing with brand new, the blowers are ok, thermostat is ok, computer diagnostic didn't show any errors...

Any ideas?

Thank you in advance,
Alain

[mjb]

Coolant temperature sensor. From your description I'm guessing the 1.8 has (at least) two of them - one for the instrument cluster gauge and another for the ECU. It sounds very much like the latter's had it