Be sure the interior light over-ride switch is not turned off or the fuse is not blown.
your knock sensor could need to be replaced
A bad coolant temperature sensor is one thing that could cause an idling speed problem with a Peugeot 406. There could also be a problem with the idle control valve.
Have an auto electrician check the crank sensor. Could however also be the fuel pump.
When the thermostat and radiator were replaced, coolant could have dripped into an electrical connector or a sensor could be disconnected or damaged. Check the temperature sensor and crankshaft sensors first.
COULD BE THE CRANK POSITION SENSOR
The new sensor could be stuck. Or the wiring could be loose, or the coolant could actually be low. Check the coolant level and the sensor wiring first.
Could be the knock sensor.
I had this problem before and it was the petrol sensor or a sensor by the filter. Or it could be your revers need turning down
Have you replaced the cam and/or crank sensor?
There is a sensor that detects temperature to turn the fan on in some vehicles, this sensor may need to be replaced.
Camshaft sensor interrupter will send that code.
intake manifold vaccum leak