1. Power Issues:
* Fuse: Check the rear window defroster fuse in the fuse box (usually under the hood and/or inside the vehicle, consult your owner's manual). Replace it if it's blown. Note that there might be *separate* fuses for the window motor and the defroster grid.
* Wiring: Inspect the wiring harness leading to the rear window. Look for any broken, frayed, or corroded wires. This is particularly important around the tailgate hinges, where the wiring is often subjected to flexing and wear.
* Relay (if applicable): Some vehicles use relays for the rear window motor. A bad relay could prevent power from reaching the motor. Consult a wiring diagram to locate the relay (if present) and test its function.
* Power switch: The power switch itself could be faulty. Try cleaning it with contact cleaner (electrical type). If that doesn't work, the switch may need replacement.
2. Motor Issues:
* Motor failure: The rear window motor itself might have burned out. This is a common failure point. Testing the motor directly (with a multimeter and applying power carefully) can confirm this, but this is best left to someone familiar with automotive electrical systems.
* Motor gear stripping: The motor's gears might be stripped, preventing the window from moving even if the motor is functioning. This requires disassembly to inspect.
3. Window Mechanism Issues:
* Window regulator: The mechanism that raises and lowers the window might be jammed, broken, or otherwise malfunctioning. This often involves wear and tear on parts within the regulator.
* Window itself: There might be obstructions preventing the window from moving – ice, debris, or even a defect in the window itself.
4. Defroster Grid Issues (if the defroster is also not working):
* Grid failure: The thin heating wires embedded in the rear window glass can break or become disconnected. This results in no heating function, and sometimes can cause the motor to draw excessive current, blowing a fuse. A visual inspection of the grid for broken lines is possible, but it can be hard to see.
Troubleshooting Steps:
1. Start with the fuses. This is the easiest and cheapest check.
2. Visually inspect the wiring. Look for any obvious damage.
3. Check the power switch. Clean it, or test it for continuity (requires a multimeter).
4. If the defroster isn't working either, suspect the grid first.
5. If none of the above solves the problem, it's likely a motor, regulator, or more serious wiring issue. You'll probably need a professional mechanic at this point, or at least detailed schematics for your vehicle.
Important Safety Note: Before working on any electrical components of your vehicle, disconnect the negative battery terminal to prevent accidental short circuits or shocks. If you're not comfortable working with automotive electrical systems, it's best to take your Tahoe to a qualified mechanic.
