1. Visual Inspection:
* Exterior: Carefully examine the rear window itself on the non-working side. Look for:
* Broken lines: Are any of the thin conductive lines in the defroster grid visibly broken, cracked, or lifted from the glass? This is the most common cause. Even a tiny break can interrupt the current.
* Corrosion: Check for corrosion around the connection points where the defroster lines meet the terminals on the window edges.
* Interior: If you can access the back of the window from inside (some Tahoes allow this), inspect for loose or corroded connections at the terminals.
2. Testing for Continuity:
This requires a multimeter capable of measuring resistance (ohms).
* Safety First: Disconnect the negative terminal of your battery before starting any electrical work.
* Access the Defroster Grid Terminals: Carefully locate the terminals where the defroster grid wiring connects to the window. This often involves removing interior trim.
* Test Each Line Segment: Set your multimeter to the resistance setting (ohms). Test the continuity of each segment of the defroster grid lines on the malfunctioning side. If a segment shows infinite resistance (OL), the line is broken in that section. You’ll need to probe along each line.
* Compare Sides: For comparison, test the same corresponding lines on the working side to get a sense of the expected resistance.
3. Repair Options:
* Repairing a Broken Line (Difficult & Rarely Successful): This involves applying conductive silver paint or epoxy to repair the broken line. This is challenging, requires a steady hand, and often isn't a long-term solution. It's prone to failure due to stress on the repair.
* Replacement Window: The most reliable, albeit expensive, solution is to replace the entire rear window. This involves getting a new window with the integrated defroster grid already installed. Expect a significant cost due to labor and the specialized glass required.
* Aftermarket Repair Kits: Some repair kits claim to repair broken defroster lines but their success rate is debated. They typically involve conductive adhesive.
4. Wiring Issues (Less Likely):
If the visual inspection and continuity test show no obvious breaks in the defroster lines, the problem might lie in the wiring connecting the defroster grid to the vehicle's electrical system. This is less common if one side is working perfectly. However, you can:
* Trace the Wiring: Carefully trace the wiring harness from the defroster grid terminals to the fuse box. Look for any signs of damage, corrosion, or loose connections.
* Check the Wiring Harness Connectors: Inspect the connectors for corrosion or loose pins.
Important Considerations:
* Professional Help: Unless you have experience with automotive electrical systems and glass repair, it's best to consult a professional auto glass repair shop. They have the tools and expertise to diagnose the problem correctly and perform the necessary repair.
* Window Tinting: If you have window tint, it's possible the tint is interfering with the defroster, though this is uncommon if one side works. The technician might need to address this.
In short, start with a thorough visual inspection. If you find broken lines, a new window is likely the best solution. Otherwise, a professional diagnosis is recommended. Don't attempt risky repairs unless you're comfortable working with automotive electrical systems and have the necessary tools.
