* Faulty Wiper Switch: While it seems counterintuitive, a malfunctioning wiper switch itself can sometimes cause the wipers to run even when off. An internal short or failure in the switch could constantly send power to the motor.
* Stuck Relay: The wiper motor is controlled by a relay. If the relay is stuck closed, it will continuously supply power to the motor regardless of the switch position. This is a common cause.
* Short Circuit in the Wiring: A short circuit in the wiring harness leading to the wiper motor can provide an unintended power path, bypassing the switch. This could be due to damaged insulation, frayed wires, or water intrusion. Look for any signs of damage near the steering column, firewall, and under the hood.
* Faulty Wiper Motor: Although less likely to cause constant operation, a malfunctioning wiper motor itself could be drawing power and engaging even when it shouldn't. This is often accompanied by other symptoms like erratic operation or noise.
* Body Control Module (BCM) Issue: The BCM is a computer that controls many electrical functions. A faulty BCM could send incorrect signals to the wiper motor, resulting in unintended activation. This is less likely but possible.
Troubleshooting Steps:
1. Check the Fuse: Start by checking the wiper motor fuse in the fuse box. A blown fuse might seem contradictory, but a short circuit could blow the fuse intermittently, leaving the circuit in a semi-functional state. Replacing the fuse will confirm if it blows immediately, indicating a short.
2. Inspect the Wiper Switch: Carefully examine the wiper switch for any visible damage or loose connections. This usually requires some disassembly.
3. Locate and Test the Relay: Find the wiper motor relay (consult your owner's manual or online resources to find its location). You can try swapping it with another similar relay (if possible) to see if the problem shifts.
4. Visual Inspection of Wiring: Carefully inspect the wiring harness leading to the wiper motor for any damage, especially near areas prone to rubbing or water exposure.
5. Advanced Diagnostics: If the above steps don't resolve the issue, you'll likely need more advanced diagnostics using a multimeter to trace the electrical circuit and check for shorts or faulty components. A professional mechanic with a wiring diagram and diagnostic tools will be necessary at this point.
It's crucial to be cautious when working with automotive electrical systems. If you're not comfortable working with car electronics, it's best to take your TrailBlazer to a qualified mechanic to diagnose and repair the problem.
