1995 Chevy Corsica Corsica check engine

Hello;
I am trying for the past four months to get this issue resolved and cannot get it done. My 1995 Corsica out of the blue flashed a code 27 quad driver failure signal. This only comes on when I drive the car at over 40 mph. If I drive below that speed no code gets activated. I did notice that since that code arose my cooling fan kicks in as if the vehicle was overheating while the temp. Gague reads a normal operating temperature. If you shut the vehicle off and restart it right away the code does not come on and neither does the fan, now I would think that if the vehicle was that hot so as to engage the fan on if you would restart the vehicle a mere seconds later the fan would kick in, but it doesnt unless you drive again over 40 mph. I tried picking the dealers head but he only would tell me to drop off the car with him, no advice no help.