1. Power and Fuses:
* Check the fuses: Locate the blower motor fuse in your fuse box (usually under the hood or inside the car, check your owner's manual). A blown fuse is the easiest and cheapest fix. Replace it with a fuse of the same amperage. If it blows immediately after replacement, there's a short circuit somewhere in the system.
* Check the blower motor relay: The blower motor relay is an electrical switch that controls the power to the motor. Your owner's manual should show its location. Try swapping it with a similar relay (if possible – make sure the amperage is the same) to see if that fixes the problem. A bad relay is a common cause.
2. Blower Motor Resistor:
* Check the blower motor resistor: This component controls the fan speeds. A faulty resistor can prevent the blower from working at any speed, including high. The resistor is often located behind the glove box or near the blower motor itself (consult your repair manual for exact location). It's usually a small, rectangular black box. Inspect it visually for any burn marks or damage. These are relatively inexpensive and easy to replace.
3. Blower Motor Itself:
* Check the blower motor: If fuses, relay, and resistor are good, the problem might be the blower motor itself. This requires access to the motor, usually located behind the dashboard. Testing the motor directly with a multimeter (to check for continuity) is recommended, but this is a more involved task. A bad motor needs replacement, which is a more significant repair job.
4. Wiring and Connections:
* Check the wiring: Examine the wiring harness leading to the blower motor, resistor, and relay for any breaks, loose connections, corrosion, or damage. A damaged wire can interrupt the power flow. Repair or replace damaged wiring as needed.
* Check the switch: The blower motor switch itself could be faulty. This is harder to test definitively without a wiring diagram and multimeter. Replacement is a possibility if other components are fine.
5. Other Possible Causes (Less Likely):
* Body Control Module (BCM): In some cases, a malfunctioning BCM could affect the blower motor. This is less common but possible. Diagnostics tools are needed to check BCM functionality.
Recommendation:
Start with the simplest checks (fuses and relay) before moving on to more complex components (resistor and motor). If you're not comfortable working on car electrical systems, it's best to take your Grand Prix to a qualified mechanic. A repair manual specific to your 1999 Pontiac Grand Prix will be extremely helpful in finding component locations and performing tests. You can often find these manuals online.
