Rear defrost turns on and off by itself!

[Aceallways]

Hi guys,

I am having a new issue with my 2002 V8 Explorer. Yesterday and today I hear a click (sounds like a relay) and then my defrost turns on/off. It can happen every 5 minutes or 20 times in 1 minute. Super annoying!

Would this be a fuse/relay that is semi-blown? Perhaps a wiring issue near the back?

It has been -20 degrees the last two days but should warm up tomorrow so I will check things out then.

Thanks so much in advance for all your help!

 

[05XLimited]

something to check is the wires that lead to the defrosting grid. They get brittle over time and it may be causing a resistance issue there. Otherwise check to see if all the connections are fully seated. If everything is tight check the relay, it may be having issues in cold weather, but may work better when it is warmed up.

 

[Exploder-Bauer44]

I had a problem with the rear defrost circuit that was similar, but became more extensive very quickly.
My question to you.....
Do you HAVE HEATED SIDE MIRRORS??

 

[Aceallways]

I had a problem with the rear defrost circuit that was similar, but became more extensive very quickly.
My question to you.....
Do you HAVE HEATED SIDE MIRRORS??

Yes I do. Both the rear defrost and heated mirrors have worked perfectly until now.

 

[05XLimited]

Yes I do. Both the rear defrost and heated mirrors have worked perfectly until now.

That creates a new source of issues. The heated side mirrors run through the driver and passenger side door boots. The wiring that is inside can get worn after a while and the wires break / short and cause tons of problems. I would check in there for any worn wiring or broken connections. Synyster has a great writeup that I followed when I had issues with my seat memory and power locks. Unfortunately the pictures are no longer showing up, but follow those instructions to check the common problem area. http://www.explorerforum.com/forums//showthread.php?t=270081

 

[Vinsanity92]

Technically we seem to all have the Heated side view mirrors pre wired. I replaced my 04 mirrors with heated versions from an 06-10 model and did not have to do anything other than plug them in for the defrost function to work.

 

[Exploder-Bauer44]

05XL knew right where I was going with that one.
I had at least 4 broken/exposed wires in my driver door rubber tube. At first it was very puzzling as to why something in the back of the truck, was affecting things in the front of the truck. I couldn't even lock my doors, because when I hit Rear Def the truck would say 'driver door open'. Then I realized, unlike my Volvo, the rear def is the same button as the hot mirrors.

I recommend finding a few short lengths of wire and crimping extensions to the inevitably broken ones you find, so they will have proper slack to not pull apart again. The only real pain of this repair is large fingers, in a small rubber passage-way. Let us know what you find!

 

[Aceallways]

05XL knew right where I was going with that one.
I had at least 4 broken/exposed wires in my driver door rubber tube. At first it was very puzzling as to why something in the back of the truck, was affecting things in the front of the truck. I couldn't even lock my doors, because when I hit Rear Def the truck would say 'driver door open'. Then I realized, unlike my Volvo, the rear def is the same button as the hot mirrors.

I recommend finding a few short lengths of wire and crimping extensions to the inevitably broken ones you find, so they will have proper slack to not pull apart again. The only real pain of this repair is large fingers, in a small rubber passage-way. Let us know what you find!

Sounds like the place to start. With the warmer weather it didn't do it yesterday, but I will pull it apart this weekend anyway.

 

[Aceallways]

Just a quick update. Yesterday my remote lock/unlock stopped working. Not sure if that is somehow related or I just need a new battery.
Anyways I removed the door panel and checked the wiring in the rubber boot as suggested. Sadly, after a thorough search I found no problems with any of the wires.
I swapped the fuse with another one in the fuse box (electric brake) and so far haven't had the rear defrost turn on or off by itself. Remote still doesn't work. Will drive around a bit tomorrow and a lot Monday so I will know if the problem still exists.

 

[Aceallways]

Reprogrammed remote and it works again. Rear defrost still turning on and off. Should I check the passenger side boot next?

 

[05XLimited]

I would go ahead and check the passenger side boot. If it is not that, then there may be an issue with the relay. The relay for the rear defrost IIRC is 2021, located in the central junction box.