Symptoms of a Bad Rear Window Defogger Switch

Reviewed by

Richard McCuistian, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Written by CarParts.com Research Team - Updated on August 11th, 2023

Reading Time: 4 minutes

Today, most modern vehicles have rear window defoggers. Rear defoggers, also called defrosters, clear condensation from your rear windows. That way, you can see behind you even if it’s foggy, raining, or snowing. You can usually control this system using a switch on your center console. When this switch fails, you most likely won’t be able to operate your rear defroster, which can be unsafe.

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Pro Tip: Some ‘60s model Chryslers had a rear defroster that was a heater core under the rear package tray with long heater hoses leading to it.

Symptoms of a Faulty Rear Window Defogger Switch

A lot of issues can arise in your vehicle’s rear defroster system, so it can be hard to diagnose the problem. However, there are a few signs of a faulty defroster switch that you can watch for.

Window Defogger Doesn’t Work

If your rear window defogger isn’t working, then it might be because of a bad switch. The defogger switch completes the circuit that powers your rear defroster. If the switch fails, the circuit won’t be able to activate your defroster, leaving your window foggy.

Driving during inclement weather is dangerous enough. Add a foggy window to that, and you’re at greater risk of getting into a traffic accident. For your own safety, replace your switch as soon as possible.

This diagram is for a 2007 Buick. Unless the vehicle you’re working on is more than 20 years old, the wiring will be similar to this. Many systems have a dedicated module with a switch and an internal timer that typically de-energizes the rear defroster after about 15 minutes or so. | Image Source: Richard McCuistian

Button Won’t Light Up

Most vehicles have an indicator light that turns on whenever you activate the rear defroster. However, if your switch is faulty, then the indicator light might not turn on. An illuminated indicator means the defroster is working, but a bad switch won’t be able to turn on the defroster, leaving the light off.

What Is a Rear Window Defogger?

Most vehicles have front and rear window defoggers. While their purpose is the same, they function differently. Your front defrosters blow hot air to your windshield through the vents of your vehicle’s heating and ventilation system. On the other hand, your rear defroster heats up your rear windows using electricity.

If you look closely at your rear window, you’ll notice thin lines inside the glass. These lines are actually a grid of wires that heat up and clear the window of fog and snow. Unlike your front defogger, your rear defogger doesn’t have to wait for the engine to warm up first. They work as soon as you flip the switch. Be careful not to throw boxes on the rear package tray because you might break one or more of the lines and render it inoperative.

What Does a Rear Window Defogger Switch Do?

You can usually find the rear window defogger button in the heater control panel. This switch allows you to easily control your rear window defogger. With the press of a button, you can clear up the fog on your rear window. Most vehicles come with a timer that automatically shuts the rear defroster off after a while.

Some vehicles also come with heated outside mirrors, some of which also activate when turning on the rear defroster.

Rear Window Defogger FAQ

What Causes a Rear Window Defogger Switch to Break?

Like other buttons on your center console, the defogger switch can wear out over time. It can get stuck when you press it too hard, or it can simply stop working. It can also become unresponsive because of a blown fuse and frayed wires. Bring your vehicle to a trusted mechanic so they can identify the root of the problem for you.

What Is the Symbol for the Rear Defroster?

The design and location can vary depending on your vehicle’s make and model. However, you can usually find defroster buttons on the center console. The front defroster button has a small curved trapezoid with three arrows in the center pointing up. Meanwhile, the rear defroster button usually has a rectangle with three arrows, like the front defroster button. In some vehicles, the word, “REAR”, is printed on the button.

Is a Rear Defogger Necessary in a Car?

Not all cars have a rear defogger. However, it’s an important safety feature for vehicles that do. Driving without a defogger on a clear, sunny day isn’t a problem, but the same can’t be said when it’s raining or snowing. If your switch fails to turn on the rear defroster, you’ll end up with a big blind spot behind you. In some cases, you might even be forced to step out of your car just to clear snow from your rear windshield. For your safety, always check if your defroster system is working.

How Much Does a Rear Window Defogger Switch Replacement Cost?

The price of rear window defogger repairs will depend on several factors. This includes your vehicle’s make, model, and product brand. On average, rear defogger switches will cost you anywhere from $10 to $210.

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