Rear Defroster Not Working? Let's Clear That Up

Stephen Fogel
December 7, 2018

The rear defroster isn’t the most crucial part of your car — in fact, some vehicles don’t even have them. 

But they sure are convenient, especially during the winter, when your windows are more likely to fog up. If yours isn’t working, it can be a safety issue — seeing out the back of the car is a good thing. So let’s look at how the rear defroster works, what can cause it to stop, and how to fix it.

How your rear defroster works

The rear defrosting is very different from the main defroster. The system consists of rows of very narrow heating elements on the inside of the glass of your rear window or hatch. These are connected to your vehicle’s electrical system and are controlled by a dashboard switch.

When the rear defrosting system is on, electricity flows through the elements and heats them up. This evaporates or melts the mist, frost, ice and snow sticking to the window. The control switch usually runs on a timer that will automatically shut off the power after several minutes.  

Reasons your rear defroster doesn’t work

While front defroster problems are often caused by issues with the cooling or HVAC systems, a problem with your rear defroster can usually be traced to a faulty electrical component. This could be:

  • The rear defroster fuse, switch, relay and wiring
  • The wires that attach to the rear defroster tabs
  • The rear defroster tabs
  • The rear defroster grid wires

Unless you have experience working on automotive electrical systems, all but the simplest diagnostic and repair procedures below should be left to a professional mechanic.   

The fuse, switch, relay and wiring

Rear defroster fuse: If the fuse for the rear defroster is blown, the defroster won’t get power. The rear defroster system draws a lot of current, so this is fairly common.

Solution: The average car owner can attempt to repair this. Check your owner’s manual for the location of the rear defroster fuse. Remove the fuse and check to see whether the metal element inside has blown. Replace the fuse with a new one of the same rating, and check whether this fixes the problem. If not, or if the fuse blows again, call a mechanic.

Rear defroster switch: The dashboard switch that controls the rear defroster system can fail, preventing you from activating the system.

Solution: A mechanic can determine whether the switch is defective and fix it.

Rear defroster relay: If the relay for the rear defroster system is defective, it can block the flow of electricity.

Solution: You can find the location of the rear defroster relay by checking your owner’s manual. If it’s loose, push it back securely into place. If this doesn’t fix the problem, talk to a mechanic.

Rear defroster internal wiring: If the internal wiring that connects the various parts of the rear defroster system breaks or gets disconnected, the electric current won’t reach the heating elements in the rear window.

Solution: A mechanic can track down any problems with the wiring in your car.

» LEARN MORE: Get an estimate for your car repair

The rear defroster wires, tabs and grid 

Wires that attach to the rear defroster tabs: If the wires that connect to the tabs on each side of the heating element are detached or broken, the defroster won’t be able to heat up and clear the glass. 

Solution: If either of the wires is detached, gently reattach the connector on the end of the wire to the corresponding tab on that side of the rear defroster grid. Otherwise, call a mechanic for repairs.

Tabs that attach to the rear defroster wires: If the tabs on each side of the heating element on the rear glass are broken or separated from the heating wire grid, the current won’t flow.

Solution: Repair kits are available online or at auto parts stores. The existing or replacement tab can be reattached to the grid with a special adhesive that conducts electricity. Again, if you’re not comfortable attempting this, a mechanic will be happy to make the repair. 

Damage to the rear defroster grid: If the rear defroster is clearing part of the rear glass, but not all of it, this could be the result of damage to the defroster’s grid lines. Any breaks in these lines will interrupt the flow of electricity to a part of the system. This can be the result of rough cleaning of the inside of the rear glass, using an ice scraper on it, or from shifting cargo.

Solution: Visually inspect the grid lines in a well-lighted area. Look for gaps in the lines where the power is being interrupted. You can get a repair kit at an auto parts store or online that will include tape to mask off the damaged area and an electrically conductive paint that will stick to the glass. Otherwise, a mechanic can handle it.

» LEARN MORE: Find a repair shop near you

Miscellaneous causes and solutions

Damage from aftermarket window tinting: If you’ve had aftermarket window tinting film applied to the rear window, it can cause problems with your rear defroster. A careless installer could damage the wiring or the tabs during installation. If you later remove the film, it can take parts of the rear defroster grid lines with it, interrupting the flow of electricity to the entire system. 

Solution: See the procedures above for identifying and solving problems with the rear wires, tabs and grid lines. You may need a mechanic’s help in fixing this. 

Damage from age and sun exposure: Over time, many uses and years of exposure to the sun, rear defroster systems can lose their conductivity. Pieces of the grid line can also flake off, interrupting the electrical flow.

Solution: Do a visual inspection of the grid lines, as well as the tabs and the connecting wires. Follow the instructions above to troubleshoot the cause. Call a mechanic if you need assistance.

Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.