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Old 10-25-2016, 08:17 AM #1
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'02 T4R Rear Defrost

Hi all.

New member with an '02 Sport, 3.4, auto... had it about 2 years.

Have searched, but couldn't find an answer -- everything I've found refers to a complete non-working defrost system (usually from rear window being down, or a bad connection.) Mine seems to be acting differently: When I hit the button on the dash, the LED indicator on the switch lights up for about 5 seconds, then goes out. Hit it again, and the same result.

Since the switch lights up, it's clearly getting power. My assumption is that it must be the relay/timer. But before I dig into it, just thought I'd ask to see if anyone had a better course of actions.

Thanks in advance.
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Old 10-25-2016, 09:52 AM #2
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Quote:
Originally Posted by tvpierce View Post
Hi all.

New member with an '02 Sport, 3.4, auto... had it about 2 years.

Have searched, but couldn't find an answer -- everything I've found refers to a complete non-working defrost system (usually from rear window being down, or a bad connection.) Mine seems to be acting differently: When I hit the button on the dash, the LED indicator on the switch lights up for about 5 seconds, then goes out. Hit it again, and the same result.

Since the switch lights up, it's clearly getting power. My assumption is that it must be the relay/timer. But before I dig into it, just thought I'd ask to see if anyone had a better course of actions.

Thanks in advance.
Well the led in the switch has a separate power source(10A gauge fuse), the relay has it's own fuses. Primarily the 15A Defog fuse.

The switch sends ground to the body ecu, which then grounds the defog relay if the back door ecu says the limit switch is closed. So yes, the limit switch IS important. Testing requires you get in to at least some connectors on the body ECU, and possibly the back door as well. Sadly the body ECU is a common failure on our trucks, for many reasons. Here is a link to the wiring diagram.
http://tacoma.site40.net/4Runner_96-...i/053rwdmh.pdf
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Old 10-25-2016, 12:43 PM #3
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Quote:
Originally Posted by IBallEngineer View Post
Well the led in the switch has a separate power source(10A gauge fuse), the relay has it's own fuses. Primarily the 15A Defog fuse.

The switch sends ground to the body ecu, which then grounds the defog relay if the back door ecu says the limit switch is closed. So yes, the limit switch IS important. Testing requires you get in to at least some connectors on the body ECU, and possibly the back door as well. Sadly the body ECU is a common failure on our trucks, for many reasons. Here is a link to the wiring diagram.
http://tacoma.site40.net/4Runner_96-...i/053rwdmh.pdf
Extraordinarily helpful info! Will start poking around.

Thanks IBall!
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Old 12-03-2016, 10:31 PM #4
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Finally getting back to this.

Here's more info:

Defrost: it sends power to the mirrors (can feel them get warmer if I cycle the defrost on a few times) and sends power to the rear window (as measured with a multimeter). But still will only stay on for about 5-10 seconds.

Rear window: the rear ECU clicks, and sometimes "chatters", but the window will not go up or down. If I unplug the harness and apply 12v directly to the motor, it will lower and raise fine.

Rear wiper: Works as it should, but moves very slowly.

This is a 2002. I took the rear body ECU out of the housing, and it is different from the pre-2001 ECU. Appears to have smaller "electronic" relays.

Would appreciate any insight from folks more knowledgeable than I.

Thanks in advance!
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Old 12-04-2016, 02:23 AM #5
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TheDurk's Rule #7 of 3G trouble-shooting: rear-end electrical weirdness is often due to broken or shorted wires in the harness between the top of the liftgate and the body. Slide that harness and look for any broken wires or missing insulation and repair.
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Old 12-04-2016, 10:37 AM #6
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Quote:
Originally Posted by TheDurk View Post
TheDurk's Rule #7 of 3G trouble-shooting: rear-end electrical weirdness is often due to broken or shorted wires in the harness between the top of the liftgate and the body. Slide that harness and look for any broken wires or missing insulation and repair.
That's a great point -- don't overlook the simple stuff. I'll certainly check that out.

But worth noting: The rear window motor gets power (as tested with a multi-meter) but seemingly not enough power to make it work. When I supply 12v from a battery directly to the motor, the window will go up and down.

The rear defogger also gets power when the dash switch is activated. But then of course loses power when the dash switch automatically deactivates 5-10 seconds later.

Thoughts?
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Old 12-04-2016, 01:09 PM #7
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Quote:
Originally Posted by tvpierce View Post
That's a great point -- don't overlook the simple stuff. I'll certainly check that out.

But worth noting: The rear window motor gets power (as tested with a multi-meter) but seemingly not enough power to make it work. When I supply 12v from a battery directly to the motor, the window will go up and down.

The rear defogger also gets power when the dash switch is activated. But then of course loses power when the dash switch automatically deactivates 5-10 seconds later.

Thoughts?
OK, two different things here. You said the rear window MOTOR get's power, but in your previous post you said you check the defroster with a multimeter. So just for clarification, how did you test the window motor getting power, and what were the readings? The rear window motor is activated by the rear body ecu but is interdependent on the Body ECU.

Secondly, the defogger is entirely activated by the Body ECU. As I explained in a previous post. If you pull the defog relay and power the defogger and it works, then the problem is most likely in the Body ECU or switch. Of course there is always the unlikely possibility the relay is bad, easy enough to switch it out. I would just check terminal 2 of the defog relay for ground when you activate the rear defog, if it goes right out, then the relay is not the problem. Allow me to remind you the rear window limit switch comes in to play. If that switch does not remain activated, the defog WILL NOT WORK.

So do as @TheDurk says and check the harness
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Old 12-04-2016, 01:11 PM #8
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Quote:
Originally Posted by TheDurk View Post
TheDurk's Rule #7 of 3G trouble-shooting: rear-end electrical weirdness is often due to broken or shorted wires in the harness between the top of the liftgate and the body. Slide that harness and look for any broken wires or missing insulation and repair.
So you should make a post with TheDurk's Rules of 3rd Gen troubleshooting, cliff notes Eye Ball engineered by yours truly.
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Old 12-04-2016, 01:51 PM #9
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Quote:
Originally Posted by tvpierce View Post
That's a great point -- don't overlook the simple stuff. I'll certainly check that out.

But worth noting: The rear window motor gets power (as tested with a multi-meter) but seemingly not enough power to make it work. When I supply 12v from a battery directly to the motor, the window will go up and down.

The rear defogger also gets power when the dash switch is activated. But then of course loses power when the dash switch automatically deactivates 5-10 seconds later.

Thoughts?
Weird is weird. So check the harness. I told you, it's a rule. I don't argue with my rules. Other rules, #6 Always swap the cable before troubleshooting a printer. #9 Always swap the plug before troubleshooting a one-cylinder engine. You don't question my rules, you just do them.

Have you tried using the key in the liftgate to operate the rear window? That bypasses the body ECU but not the Back-door ECU or the power supply. So that's an important data bit. Sorry if you reported it and I missed it.

Don't forget, you have to turn the key and hold it for a few seconds before the window operates.
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Last edited by TheDurk; 12-04-2016 at 01:57 PM.
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Old 12-04-2016, 03:00 PM #10
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Quote:
Originally Posted by IBallEngineer View Post
So you should make a post with TheDurk's Rules of 3rd Gen troubleshooting, cliff notes Eye Ball engineered by yours truly.
Problem is I forget most of them after I make them until the same thing comes up and I regret not following it.
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Old 12-18-2016, 12:06 PM #11
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i am kinda having the same issue...my back window goes up and down, wiper works fine, defrost light stays on for 15 min then shut off like normal but will not defrost window.. what should i look into?
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Old 12-18-2016, 01:41 PM #12
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Quote:
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i am kinda having the same issue...my back window goes up and down, wiper works fine, defrost light stays on for 15 min then shut off like normal but will not defrost window.. what should i look into?

Assuming you checked the 15A defog fuse correctly. You need to check the actual defroster wire on the back light. Here is the FSM method.

http://tacoma.site40.net/4Runner_96-...defsy/insp.pdf

Or you can pull the rear door trim and check the actual connections, you need to have power AND ground. Here is the EWD for an 02.

http://tacoma.site40.net/4Runner_96-...i/053rwdmh.pdf

Easy Peasy!

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Old 12-18-2016, 01:42 PM #13
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Forgot to add, I have the same problem on my 99. But I'm too lazy to check it, and besides. THIS IS CALIFORNIA!

heh
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Old 12-18-2016, 01:59 PM #14
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Quote:
Originally Posted by IBallEngineer View Post
Assuming you checked the 15A defog fuse correctly. You need to check the actual defroster wire on the back light. Here is the FSM method.

http://tacoma.site40.net/4Runner_96-...defsy/insp.pdf

Or you can pull the rear door trim and check the actual connections, you need to have power AND ground. Here is the EWD for an 02.

http://tacoma.site40.net/4Runner_96-...i/053rwdmh.pdf

Easy Peasy!

thank you for the info!!
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Old 06-22-2017, 09:39 AM #15
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I always appreciate it when folks "close the loop" by posting back with the final solution to their problem. So here's the update on this. Pulled back the rubber boot on the wire harness to the rear hatch. Per Durk... this was the problem:





This has been a garaged, well maintained vehicle its whole life. Lived in the Maine since new, not Southwest or somewhere else with crazy sun and oppressive heat. The wire insulation on every single wire pair is cracked/compromised. Also, this is a 2002 -- so the newest 3rd Gen possible.

Maybe not a bad idea to check your wire harness before you start to have problems.

Edit: not sure why the pics don't show. Right click on the link and "open in a new tab", and the pic loads. (?)

Last edited by tvpierce; 06-22-2017 at 12:31 PM. Reason: Image links not working
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