Back Window Rolls Down on its Own at Random Times

[WrenchTech]

My back window, the one in the tailgate, has a mind of it’s own lately. The problem is that it rolls down on its own a random times. I rolled it up twice yesterday and found it rolled down an hour later both times. This condition seems to be affected by the sun. When it is cold and cloudy it happens much less.

When I bought the 4runner the window didn’t work work at all. The owner told me the window regulator box needed to be replaced. I picked one up at a pull-your-part wrecking yard for $25. When I took the interior cover panel off of the tailgate I found that the box was unplugged. I replaced that box with the one I purchased, buttoned things up, and was pleased to have a working window.

That was when the window started its random operation. It then made sense to me that the former owner had left the box unplugged because he was probably experiencing the same problem.

The problem gets worse when the sun is shining on the tailgate warming it. It will also do it when I open or close the tailgate. This make me think that the problem is due to a fault in the wiring.

So the question is do I have two control boxes with the same problem, or is the problem due to something else, like a short in the wiring?

 

[mtbtim]

You probably have partially severed wires going from the body to the hatch. You need to investigate. This video will help you out.


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[Sarki]

More than likely the wiring harness for your tailgate has some cracked/broken wiring, not uncommon after many years of opening & closing the tailgate.
Fortunately there’s a video made by Timmy the Toolman that addresses this exact issue.
Rear Hatch Wiring Repair (3rd Gen 4runner) - YouTube

 

[mtbtim]

More than likely the wiring harness for your tailgate has some cracked/broken wiring, not uncommon after many years of opening & closing the tailgate.
Fortunately there’s a video made by Timmy the Toolman that addresses this exact issue.
Rear Hatch Wiring Repair (3rd Gen 4runner) - YouTube

I guess I just beat you with my post. Thanks for mentioning my video.

 

[Sarki]

I guess I just beat you with my post. Thanks for mentioning my video.

Tim your videos have helped and encouraged me countless times and I appreciate all the time and effort you put into this site to help the community.

 

[WrenchTech]

Thanks to everyone for pointing me in the right direction on this issue. I am amazed again at the richness of Timmy the Toolman YouTube video resource.

 

[Jakeepoo3]

Thanks to everyone for pointing me in the right direction on this issue. I am amazed again at the richness of Timmy the Toolman YouTube video resource.

Sounds like a circuitry issue. Can you recreate the problem by your own will? If so put a test light or multimeter on the connector to that controller box. That's if you don't see the problem in the harness boot. Someone the other day had a similar problem with battery voltage pulsating at that connector.

 

[Bad Luck]

Thanks to everyone for pointing me in the right direction on this issue. I am amazed again at the richness of Timmy the Toolman YouTube video resource.

I had a similar problem with my first 4Runner. I would come out to the rear window being rolled down with no rhyme or reason. I thoroughly inspected the wiring harness between the body and rear hatch but never found any problems. What fixed it for me was gluing the rear hatch button part of my key fob to where it couldn't depress at all. Maybe it was a coincidence, but it never happened again for the 15 months after I did that until I sold that 4Runner.

 

[sportscarfan]

Whenever this topic comes up I repost my experience - (not broken wiring, not control box)
https://www.toyota-4runner.org/1471503-post5.html

 

[96RedRunner]

[MENTION=147057]WrenchTech[/MENTION] I had wires broken and not the insulation, diagnosing not always cut n dried easy to see.

[MENTION=319302]Bad Luck[/MENTION] had pocket lint build up in fob buttons cause stuff.

 

[Brakleen Sniffer]

I really fixed it!

My 2000 4Runner started randomly rolling the rear window down by itself. My version of this problem also disabled window up/down from the tailgate key switch, and also disabled the rear wiper, so I couldn't just disconnect the window motor. Not that I was willing to do that anyway.

tl;dr A new rear window switch assembly fixed the problem. p/n 84830-35041. This is the electrical switch piggybacked onto the tailgate key lock cylinder.

First, know that the Toyota service manual has many errors. Test voltages listed for the rear ECU are wrong, there are wires in the tailgate that are not shown in the manual, and the descriptions of how things are supposed to work are very poorly written (or translated?). So those things made it hard to know WTH to look at.

- I checked the wires in the tailgate flexy boot - not the problem.
- I tried a new used rear ECU. No.
- I pulled the ECU PC board and tested it on the bench. Applied 14V and ground and all other pins floating. Works: up and down relays click when pins 9 and 10 are grounded.
- Reinstalled the ECU in the vehicle with all tailgate motor and sensor connectors open. Works, so the problem must be one of them, and the problem is not bad data coming down the MPX serial data wire from the body ECU.
- Reconnect connectors one at a time, and failure occurred when I clicked the key lock switch connector into place.
- Turns out that there was an 80 ohm "short circuit" in the switch between the "window down" wire and ground. Evidently this confused the ECU. To check this, pull the ECU connector and on the wiring bundle measure pin 9 to ground and 10 to ground. Don't do it with the connector installed because there's power applied to the ECU full-time, which may confuse the ohmmeter.

Like all completed troubleshooting, this sounds easier than it was. There's the physical difficulty of reaching some of the electrical connectors, the misleading service manual, too many things to check, and my short attention span which caused me to jump around instead of pursuing each clue.

I hope this helps someone. It was therapeutic to write.

 

[Malcolm99]

Like Brakleen, the key switch has full time power, if it is compromised, any excessive moisture will roll the window down on its own.

 

[phattyduck]

Like Brakleen, the key switch has full time power, if it is compromised, any excessive moisture will roll the window down on its own.

That's a good theory. That explains why the once or twice it has happened to me it was also (luckily lightly) raining.

-Charlie

 

[Brakleen Sniffer]

No doubt moisture could cause this. The switch has an O-ring that’s supposed to keep the contacts clean, but eventually everything leaks.

The green disk is keyed to the back of the lock cylinder and rotates to connect the up and down wires to ground.

FWIW, in my switch the short circuit was in the sealed part of the switch. It was there even after disassembly and cleaning.