Hi and Welcome to Just Answer!
it sounds like engine computer has lost power or communication.
cooling fan will come on as safety future
if you have another car there disconnect computer with ignition in on position and fan should come on at high speed.
how do i get the fan working normally again .
you need to scan the vehicle for fault codes. also check engine computer power supply circuits.
i have fault code 0750 self adaptaion of mixture formation for enleanment left cylinder bank.0521 diagnosis tumble flap "intake manifold " short circuit to ground tumble flap sticks in actuated position . 0746(p0172) self adapation of mixture formation for enleanment at idle for right bank is below permissible limit .2092 mixture in right bank is too rich when idling . 2096 the mixture in the left cylinder bank is too rich when idling . 1337 alternator serial interface. All these codes were presnt when I initially scanned the vehicle but besides the alternator code didnt see why it would keep the fan running at high speed hence the reason for not mentioning it earlier . the car starts and runs (do you still want me to check computer power supply )
yes check computer power supply and 5V reference voltages. if codes are present with engine not running, there is problem with electricl system
i will do as you say tomorrow , with the power supply and reference voltages one final question . if the power supply and reference voltage is ok but the fan still runs at high speed are there any other suggestions .
if it works high speed without engine running and all circuits and cignals OK. -ENGINE COMPUTER FAULT