* Faulty Blower Motor Resistor: This is a common cause. The resistor controls the fan speeds. If it fails, it can short-circuit and cause the motor to run at full speed all the time. Inspect it for any burn marks or other signs of damage.
* Short in the Wiring Harness: A short circuit in the wiring leading to the blower motor or the control switch can bypass the relay and resistor, causing the motor to run continuously. Carefully inspect the wiring for any frayed wires, melted insulation, or areas where wires might be touching.
* Defective Blower Motor Switch: The switch itself might be faulty, stuck in the "on" position, or internally shorted. Try disconnecting the switch to see if the blower motor stops. If it does, the switch is the likely culprit.
* Problem in the Climate Control Module (CCM): The CCM is the "brain" of the climate control system. A malfunctioning CCM can send incorrect signals, leading to the blower motor running continuously. This is less likely but possible. Diagnosis requires specialized tools or a scan tool.
* Grounding Issue: A poor ground connection somewhere in the system can cause erratic behavior, including the blower motor running constantly. Check all ground points associated with the blower motor and its circuitry.
Troubleshooting Steps:
1. Disconnect the blower motor: This is the safest first step. If the motor stops, you know the problem is within the electrical system, not the motor itself.
2. Inspect the Blower Motor Resistor: This is usually located behind the glove box or under the dash. Access it and check for damage. Replacing it is a relatively easy fix.
3. Visually inspect the wiring harness: Look for any signs of damage, especially near the resistor, motor, and switch.
4. Check the Blower Motor Switch: Disconnect the switch and see if the motor stops. If so, replace the switch.
5. Check the Ground: Locate the ground wire for the blower motor and ensure it's clean and securely connected.
If you're not comfortable working with car electrical systems, it's best to take your Cadillac to a qualified mechanic. Diagnosing electrical problems can be tricky, and improper repairs could lead to further damage or even fire hazards. A scan tool might be needed to rule out more complex CCM issues.
