Fan speed 6000 rpm - REALLY new logic board needed?

15" - late 2008 mbp.

past few months, fan speed continuously @ 6000 rpm, cpu usage normal.

i've tried:
- resetting pram & smc
- running hardware diagnosis (no errors)
- controlling speed multiple applications (e.g. fan control)
- reinstalled os






it's driving me crazy. mean need spend €800+ on new logic board looks tiny broken temperature sensor?

ideas / suggestions appreciated!

 

if told true. if no software solution helps hardware not repaired exchanged.

computer electronics aren't old cars. cannot fix stuff. identifiy part has fault , exchange it.
problem in notebook sits on logicboard , 1 piece practically impossible repair if 1 thing doesn't work. have switch whole.
chip once soldered logic board can never exchanged @ least not effort not more costly new part. quite sure same sensors. if 1 of integrated ones.
cable got loose repairs or contact bad, else cannot repaired. if nobody took apart , loosend cable or attached badle there nothing repair.

 

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