Ever Noticed Those Lines On Car Rear Windows? Here's What They Do

If you ever find yourself questioning how certain elements of your car function, such as how electronic parking brakes work, then you may wonder what the lines your vehicle's back glass are for. Not all cars have this feature, but, today, most do. The lines are usually horizontal but can also be in a grid pattern, and without them you might have difficulties driving safely, especially in inclement weather. That's because they're crucial elements of your vehicle's defrosting system, referred to as the rear defroster. 

While the front windshield defroster is part of the car's HVAC system and blows hot air through vents on top of the instrument panel to clear ice and fog, the rear defroster uses electrical current to produce heat to clear the back window. The lines are actually thin wires made out of conductive materials like metal or electrically conductive resins, and they are either attached to the inside of the glass or embedded within the glass during manufacturing. Sometimes, you'll find similar defroster wires in rear side windows of SUVs and on the lower edge of the windshield, underneath the wipers; There are some luxury vehicles that use this process to offer heated side front windows and heated windshield functionality, and in the 1980s, Audi cleverly used the rear defroster to spell out its "quattro" branding.

Like any component or part in your vehicle, the rear defroster can malfunction and stop working, which could be hazardous when driving in cold weather. Broken electrical connections are the common culprit when dealing with an inoperative rear defroster, which can be the result of an unplugged harness or physical damage to the window (like scratches or corrosion). Overall, other than avoiding scratches and harsh, corrosive chemicals, there's generally no special care required for cleaning back windows with a rear defroster system. That being said, aftermarket window tint can impact the effectiveness of this feature, and it may cause bubbling and/or discoloration in the tint itself.

If you don't see any lines on your vehicle's rear window, there's a good chance your vehicle just doesn't have a rear defroster, which is usually the case on older, base-model cars. On some newer cars, advancements in safety have resulted in rear defrosters being less noticeable than in the past due to the use of less-visible materials or ultra-fine wires. Similar to these defroster wires, there may be other components in your vehicle that you are curious about. For example, that circle on your car's dashboard is really a sensor, here's what that shark fin on top your car does, and here's what that HDMI port in your is actually for.