ECM/cooling fan

I have a 1989 Buick lesabre 3.8. The cooling fan never turns off even when its 36 degrees Fahrenheit outside. I changed the Coolant temp sensor but the fan still keeps running even when I first start it up in the morning. I recently bought a Actron scanner and it said the ECM thinks its -39 degrees! and gives a code 15 Engine coolant temp error/low voltage. I checked the reference voltage to the senor and its normal. My logic is if the car thinks its -39 F it would not have the engine fan on but it does. Any help would be greatly greatly appreciated. thanx

Your car is designed so that if the ECM cannot decide what the real engine temperature is... that it will always turn on the cooling fan to be safe...You would not like it if while it thought the engine temp was minned out at -39 degf that the engine truly did overheat...so it plays it safe by design and turns fans on. Also the code must be reset (unhook battery or use scan tool) to turn fans off.

Did the coolant temp sensor you changed have 2 wires? yellow and black? Black should be a ground, the yellow a 5v reference voltage. Do you have these conditions? Is connector plugged in correctly, are wires making continuity to connector? Code 15 is a wide open (not plugged in) code...

Double check your sensor plug.

Yes the wires are black and yellow and its installed correctly. I hooked the volt meter to it and got a 5v reference signal. I have unhooked the battery and pulled the ECM fuse but the code is still their with the fan running. I also went to napa and got a referb ECM no change. I also installed new relays. Is it possible to have a good reference voltage but not communicating to the ECM? Im at the end of my rope. I spent the last year restoring the car only to have this crop up. Do you have any other ideals on what the problem could be. Thank you so much.