I have yet to see an 850 window motor fail. I have however seen MANY switches fail. Next time it won't go up, try hitting the switch repeatedly many times. Bad contact inside the switch can sometimes be overcome by rapid repeated activation. If it goes up during this test, it's your switch. Problem is they are an assembly and you have to replace the entire center console window switch assembly. Another way to verify a motor problem is to remove the door panel and conect a voltmeter to the window motor conector. You should read 12 volts in either switch position but the polarity will switch from + to - when switch is moved up or down. If the voltage is there and the motor does not work, needs motor. Motor is attached by 4 bolts and is easy DIY repair. If they tell you you have to buy a regulator to get the motor, get a used part from a bone yard.