* Blower Motor Itself: The blower motor might be failing. Intermittent operation is a classic symptom of a worn-out motor's brushes or windings. It's getting power sometimes, but the internal components are failing to maintain consistent operation.
* Wiring and Connections: Even with a new resistor, there could be a problem with the wiring harness leading to the blower motor. Look for broken wires, corrosion on connectors, or poor connections at the blower motor itself. Pay particular attention to the area where the wiring harness is routed near the blower motor, as it can be subject to wear and tear.
* Blower Motor Switch (Again): While you haven't mentioned replacing it directly, the blower motor switch itself could be the culprit. It's possible the switch is failing internally, causing intermittent contact. It's a possibility even if you've replaced the resistor.
* Body Control Module (BCM): The BCM controls many electrical functions in your car, and a faulty BCM could be sending inconsistent signals to the blower motor. This is a less likely scenario, but it's possible. Diagnosing a BCM problem usually requires a professional scan tool.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine all wiring and connectors related to the blower motor, resistor, and switch. Look for any obvious signs of damage, corrosion, or loose connections. Pay close attention to the grounds.
2. Test the Blower Motor: If you have a multimeter, you can test the blower motor directly for continuity and resistance (refer to your car's repair manual for specific resistance values). This will help determine if the motor itself is bad.
3. Check for Power at the Blower Motor: With the ignition on and the fan switch in different positions, use your multimeter to check for voltage at the blower motor connector. You should see voltage present at the correct terminals when the fan should be running. If the voltage is inconsistent, it points towards a wiring or switch issue.
4. Check the Blower Motor Switch: If you can access the switch easily, try tapping on it gently while someone operates the fan switch. If the fan starts or stops inconsistently during tapping, it suggests a faulty switch. This is often difficult to diagnose without replacing the switch.
5. Professional Diagnosis: If you're not comfortable working with electricity or if the problem persists after these steps, take your Grand Prix to a qualified mechanic. They have the tools to diagnose more complex issues like a faulty BCM.
Remember to disconnect the battery's negative terminal before doing any electrical work to prevent shorts or injury. Always refer to a repair manual specific to your 2003 Pontiac Grand Prix for detailed wiring diagrams and component locations.
