Any reason why the rear defroster would just quit working on my 2011 F-150, I havnt checked anything yet, but Im guessing a fuse...

I also noticed that my rear power sliding window has really slowed down when closing, now I see it runs on a cable, Is there anything that should be lubed?

 

Where do you live that you have tested the rear defroster already?

 

In Canada Near Ottawa. Wasn't trying to get rid of frost though. The rear defroster is tied into the heated mirrors, it was chilly and Foggy here so my mirrors kept fogging up...

 

I use my mirror heaters quite a bit to clear condensation from dew in the mornings lately. It was on the rear window? Mine has connections on the side lower corners.

 

Im pretty sure my "Rear Defrost" button also controls the mirror heaters, although I could be wrong. Anyways, they were working today so Im thinking there must be some sort of temp sensor and it has to be below a certain temperature outside in order for the rear defrost and mirror heaters to work...

 

A few days ago went to turn on the rear defogger and got no light on the control button and no defog. Tried several (hundreds?) of times with no success. I checked the fuse, checked the relay, checked the connections to the element, slid the window open and closed many times with no success.

Searched the internet for answers and found a few references to a solution involving replacing the entire rear window (if I understood correctly there's a position sensor as part of the assembly). As the truck still has some factory bumper to bumper warranty left I made an appointment for service for tomorrow.

I kid you not, as the wife and I left this afternoon to drop off the truck, I tried the defogger and, viola, it worked (at least the light did). Cycled several times while opening / closing the slider and all worked as expected. So, I cancelled the appointment and will keep an eye on it for now.

I really hate things like this but won't complain if it never comes back.



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I did all the same things as you ^^^, Im thinking it has to be below a certain temperature in order for the rear defrost to work...

 

No rear defrost this morning. Guess I'll be troubleshooting again this weekend.


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I had a similar problem with my 2011 FX4 last year. Long story short, the window was closing passed the defrost contact points. Easy fix was to close the window fully then back the window up about 1/16" or less. Works every time now.

 

Well, did some more troubleshooting and found that there's 14.8 volts across the rear defrost grid when I press the defrost button (still no light). Repeated presses of the switch toggle the voltage from 14.8 to 0.

I disconnected both power and ground leads from the grid and measured the resistance as virtually infinite. So, there's voltage present but no current possible. Cycling the sliding window several times yielded no change to the resistance. However, pressing the slider at the contact cover point did cause the resistance to drop to around a few ohms (enough for the continuity tone on the meter to sound).

From what I've read online and my best guess... when the slider is closed it completes the defrost circuit by virtue of two contacts on the driver's side pane and the slider. The yellow lamp on the dash lights up if the circuit is complete, and goes out otherwise. The high resistance I measured probably explains why my indicator lamp does not light up anymore.

These contacts on the slider may be "worn", "loose", "dirty" or whatever thereby preventing the defrost from working properly. I'm not sure what to do next at this point as the contacts are not accessible and I do not want the dealer ripping out the glass just yet as I feel the truck may never be the same.

It would be great if there were a simple way to bypass the contacts and just have the two rear side panels work.


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This is what I'm thinking. $1700 to change the rear window. Not happening. Can I bypass the window so my mirrors will defrost? The window will clear up with heat from the cab.

 

I guess I'm surprised the design is so poor that a failed (open) rear defrost would prevent the rest of the system from functioning.

As an electrical engineer I can surmise a way to fool the system into thinking the rear defroster is functional (with some large power resistors) but I dont think it would be practical.


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Plus, I think it's fair to say that you shouldn't have to 'fool' the system on an item that should be working.

Disappointing that so many are having this problem -- me included...

 

Wondering if a jumper wire bypassing the rear window would at least allow the heated mirrors to work.

 

What you really need to do is to get someone to measure the resistance of the heater on a functional rear window (while it's turned off). Then disconnect one side of it and insert an amp meter into the circuit and measure the amount of current with the heater turned on. With those two values, you can select the proper resistance and wattage values of a bypass resistor. I suspect Ford wired all three heaters in series as a cheap and easy way to limit the current flow. If so and you just bypass one heater with a piece of wire then you'll overload the other two heaters and burn them out!