Bill, there are 2 possibilities of what could be going on here. 1st, it is very commonly reported now from other GP owners that the ignition switch can begin to fail as these cars age. This is a definite design flaw in the 6th Generation Grand Prixs (1997-2003) One telltale sign that the ignition switch is on its way out is that the fan speeds will stop working on #1 through #4. The fan will resume working on #5 setting. Have you checked the cars headlights when you turn the fan to 1-4 settings? If the headlights go out when fan is on 1-4, then it is the ignition switch for certain. The fan and headlights will work normally when set to #5. Easiest way to check this is to park facing a wall. Turn on the headlights from the switch. Then cycle through the fan speed settings and observe the headlights. The switch is located on the steering column. A new switch can be bought from https://www.amazon.com/ACDelco-D1491...for+grand+prix. Detailed instructions can be found on http://sparkys-answers.com/2009/09/2...-changing.html
Another possibility is that the fan blower resistor is going bad or has gone bad. Many report that when the fan stops working from speed 1-4, and works on 5, then the resistor is faulty. The resistor is located on the passenger side footwell under the dash. A new resistor can be purchased from https://www.amazon.com/ACDelco-15-80...for+grand+prix
