* Broken Heating Element: The most common cause. A break in the thin wires forming the grid within the rear window stops current flow to that section, leaving it unheated. This is usually a permanent failure requiring replacement of the rear window.
* Blown Fuse: Check your owner's manual for the fuse relating to the rear defroster. A blown fuse is an easy fix, just replace it with the correct amperage fuse.
* Faulty Relay: The defroster system often uses a relay to switch the high current needed for the heater. A bad relay will prevent the defroster from working. This might require replacing the relay.
* Wiring Problem: A break or short in the wiring leading to the rear window could also prevent it from working. This is difficult to diagnose and repair without experience in automotive electrical systems.
* Bad Defroster Switch: The switch itself could be malfunctioning. This is less common but possible.
Troubleshooting Steps:
1. Check the Fuse: This is the easiest first step. Replace it if blown.
2. Inspect the Rear Window: Carefully examine the rear window's defroster grid for any obvious breaks or damage. Look for sections that aren't heating up.
3. Test the Switch: Try the defroster switch multiple times. If it feels loose or unresponsive, it might be faulty.
4. Check the Relay (if accessible): Locating the relay requires consulting your owner's manual or a wiring diagram. You might need to test it with a multimeter to determine if it is functioning correctly.
Important Considerations:
* Safety First: Disconnect the negative battery terminal before doing any electrical work on your car. This will help prevent accidental short circuits or shocks.
* Professional Help: If you're uncomfortable working with car electrical systems, it's best to take your Probe to a qualified mechanic. Replacing a rear window is a more advanced repair that requires specialized tools and techniques.
In short, you can't "unfreeze" a frozen defroster grid; you need to find and fix the underlying electrical problem. The problem is almost certainly a broken heating element in the rear window, requiring a replacement. Start with the simpler steps (fuse check) before considering more advanced troubleshooting or repairs.
