Rear Window Defrost: Root Cause Repair
Greg

Avondale, Canada

#42 Mar 30, 2010
LMAO so you know what it was???? i tore anything and everything that i could apart (after checking the clips on the rear windshield for continuity; which there was none, and checking the connector in the front) could not find anything, power going in, no power coming out, just ground.... so im sitting there thinking wtf?! then im like hmmmm ill try and check for continuity on the windshield itself, sure enough it was fine.. so then i check clip to clip again, nothing. After that i checked windshield to drivers side clip, sure enough there was continuity.... then im like ok... so i go in for a closer look at the passenger side clip (where it connects to the rear windshield) and guess what? someone JB Welded the clip back onto the rear windshield...-.- i don't even know what to say lol, other then JB Weld DOES NOT conduct electricity!!!!!! thx for the help guys :)
mar

AOL

#43 Mar 30, 2010
Greg... just when I thought I had heard them all, that's a new one. Good find!
Bob

Winnipeg, Canada

#45 Jul 12, 2010
Fantastic, repair worked great. Thank you from a cold Canadian who uses his Rear Window Defroster way to many months out of the year.

(03 cavalier)

thx again.

bo
RJL

Richmond, Canada

#47 Oct 4, 2010
Just fixed our 2002 Cavalier as per your instructions. Great post! Thanks!
Chuck

Ogden, AR

#48 Nov 21, 2010
I am also having a problem with my Rear Window Defroster on my '98 Cavalier. When I press the button, the following three things happen:

1. I can hear the relay click
2. The LED comes on
3. It stays on for the given amount of time

But, the defroster will not kick on. So I tried the simple things first. I reseated the two connectors on the back glass. I also checked (visually and with a multimeter) and reseated the fuse. Then I came across this post. So I took the connector apart. All wires and pins seemed in good shape. However I decided with me having the same symptoms as everyone else here, that I would go ahead and bypass the connector and hook the bigger purple wire into the black wire. That still didn't fix my problem. Now here is the weird part... When I test the voltage coming out of the purple wire (with the car started and the Rear Defroster on), I only get 1V?! I have tested it about 10 times. This can't be right, can it? I have used different grounds (including the battery). I have even cut the end off the purple wire just to make sure it wasn't 'bad' and tested a 'fresh' piece of the wire. I thought the multimeter was acting up, so I tested other things. The meter is fine, for whatever reason the purple wire is still only outputting 1V. Does anyone have any idea what this means?

-Thanks
Musicdan

Halifax, Canada

#49 Nov 23, 2010
THANK YOU 1000 TIMES!! I read your post 20 minutes ago and now I'm responding with a working rear defrost. I was able to cut the 2 wires close enough to the connector that I had enough slack to twist them directly together and put a good blob of solder to them.
My girlfriend's father's car is doing the same thing.. looks like I'll be scoring some brownie points!!:D
MAR

Hinesburg, VT

#50 Nov 23, 2010
Hi Chuck... I have been thinking about you reported symtoms. A reading of 1V is strange and really makes me suspect a floating line or bad gnd. I don't have a 1-2-3 follow these steps solution for you but please try and explore these ideas.

1) Use a long wire to tie the neg(blk) meter probe directly to the neg battery terminal to ensure a good gnd for measurments. I ALWAYS use this method since having been tricked with bad gnd connections in the past.
2) Than probe both legs of the defrost fuse w/fuse installed you should be able to to access both legs via the top of fuse on the exposed metal.(defrost off, key on but car not running). Should have +12v. Assuming you have full 12v present on both sides of the fuse means pwr present and fuse is good. Next turn on the defrost and ensure that you still have pwr(12v) on both sides. Might see a slight drop in meas voltage but should high(~12v) and not low(ie 0v-10v).
3) I think (but not 100% sure) that the defrost LED is powered on the down stream side of the defrost relay(in dash). The fact that the LED is on makes me believe that you are getting pwr through the defrost cntl unit and its just not getting to the rear window. Maybe the connector/wire in the back of the cntl unit is bad. You may have to take the dash apart in order to get access to the defrost relay which is mounted directly behind the defrost button. But before that please...please make sure you really don't have pwr on the feed wire down under the carpet. Using a needle or piercing probe try to probe that wire some distance away from the typical suspect connector(under carpet).
jim

Whitecourt, Canada

#51 Nov 23, 2010
Excellent post, I have a 2002 and I had the same problem. I fixed it in 10 minutes with your directions. You probably saved me $200.00 or more at the mechanics.

I beleive the cause of my problem was that moisture has caused corrosion in the connector. The wires need plenty of power and the corrosion gradually depletes the ability to transmit the power.
Thanks again Mar
Patty

Acme, PA

#52 Nov 27, 2010
I'm having problems with my defroster also,..2003 cav,..but my problem is when I push the button in, it won't stay in. Any ideas?
MAR

Hinesburg, VT

#53 Nov 29, 2010
Patty wrote:
I'm having problems with my defroster also,..2003 cav,..but my problem is when I push the button in, it won't stay in. Any ideas?
I will have to look tonight but if I recall correctly the button is NOT designed to stay "pushed in". I think it's a momentary push button that simply triggers the electronics to start a defrost cycle. In other words when you release it, the button will return to it's out position. Does the yellow/green LED light turn on when you push and release the button. If not check the fuse. Either way you should apply my the fix to bypass the connector since it is more than likly bad.
mar

Fitchburg, MA

#54 Nov 29, 2010
Patty wrote:
I'm having problems with my defroster also,..2003 cav,..but my problem is when I push the button in, it won't stay in. Any ideas?
I checked and it is a momentary switch. You push and release. It does not stay pushed in when you release. You abort a started cycle by push and release a second time.
Brandon

Mobile, AL

#55 Dec 9, 2010
Ok, I've read your fix, no luck. started probing around. My green connector with the purple wire does NOT look burnt or melted in any way. With a multimeter I get a solid 14.6 volts at the connector on the drivers side back window, and if I connect my meter to the battery and touch to passenger side "ground" I also read 14.6 volts. also get the same voltage at the green connector under dash. I can always tell when window is pulling juice cause it puts a little more strain on the motor when you turn it on,(at idle.)
so I ran a jumper from the battery to the drivers side of the rear defrost, you could tell it "turned on" cause the small arc at the end of my wire and you could hear it in the engine.
How is it that I am getting the proper voltage, but the defrost does not work on its normal circuit. I also tried running the jumper wire from the green connector under dash to the drivers side rear window... no luck, seems problem is higher up than this green connector, what else to check (cause original circuit is still sending voltage)?
Any help, much appreciated.
Thanks
Brandon
Brandon

Mobile, AL

#56 Dec 9, 2010
after more probing....
i'm getting 14.5 volts at back drivers side, then when I plug in the passenger side it goes to zero.(makes sense) and same power check when I switch over and check passenger side. It's like there is not enough current or something.
push button, hear click, and light turns on, auto shutoff after 10/15.
Engine does not surge like it used to when you turned on rear defrost, but it does if I run a hot jumper to the rear drivers side terminal on back glass.
Thanks agian in advance.
MAR

Hinesburg, VT

#57 Dec 10, 2010
Brandon wrote:
after more probing....
i'm getting 14.5 volts at back drivers side, then when I plug in the passenger side it goes to zero.(makes sense) and same power check when I switch over and check passenger side. It's like there is not enough current or something.
push button, hear click, and light turns on, auto shutoff after 10/15.
Engine does not surge like it used to when you turned on rear defrost, but it does if I run a hot jumper to the rear drivers side terminal on back glass.
Thanks agian in advance.
Drivers side voltage should NOT drop to 0V when you tie PS to gnd. When the grid is energized (ie gnd on PS & pwr on DS) you should be measuring approx +12v(14v is ok) across the window grid (ie 12v meter reading with PS(gnd) to DS(high)). Two possible reasons why the DS is dropping to 0V when you energize the grid.
1) The resistance is too high in the connectors/wires which feed the grid. When the resistance is high than the voltage will get dropped across the parasitic resistance along the way and wont make it to the grid. I dont care what the connector under the carpet "looks like". If you haven't yet applied my bypass fix than please do so because it can be the cause of high resistance.
2) The available current output of the driver ckt is too low and thus the low resistance grid is dragging down the ckt output.

The reason the engine isn't bogging down any more when you energize the ckt is because the high power(low resistance) load assoicated with the grid isn't getting the current it needs(because of #1 or #2 above) and thus isn't loading the electrical system.

1st apply my fix and if that still doesn't work try the following. With everything hooked up and the grid connected and a defrost cycle energized lets assume the DS grid still meas 0V(ie still broken). The idea is to pierce probe the DS wire all the way back to the source until you fins the point where the volt reading changes from 0v to +12v. At that point you know where the high resistance defect is .

let me know
Brandon

Mobile, AL

#58 Dec 11, 2010
Ok, I've done your fix, soldered it up nice and secure. Still no luck.
Now before I connected the wires I ran a jumper from the battery to the black wire after I cut it from the green connector, and the window worked.
So my problem being upstream of where the green connector used to be... I'm assuming is at a connector or device of some sort becuase I feel doubtfull that it is somewhere in the middle of the bare wire. Seems all there is, is a relay and a timer, is all of this in the back of the heater controls unit, and is there anyway to test this before removeing the unit.
Also, the switch does work, the light turns on, and you can hear the relay click, and it shuts off after 10/15 min. I do read voltage if the back PS connector is off, it is pretty much 0 if it is connected.
Any other advice before I start into the controls in the dash.
Thanks
Brandon
mar

Saint Albans, VT

#59 Dec 12, 2010
The fact that the led light works and you hear the relay click seems to indicate that you are getting pwr to the timer ckt. I think you are going to have to take the dash apart to get at the timer relay. Could be the connector in the back of that unit. Get a Haynes manual it lays out the steps well. I have done it before. Its not hard but does take time,lot of steps. Besure to disable air bag ckts per Haynes manual before playing in dash ckt
Corey

Tacoma, WA

#60 Dec 14, 2010
Thanks hopefully that's all that's wrong with mine. I would have never thought to look there. I have ripped out almost all of my interior but didn't look there
Corey

Seattle, WA

#61 Dec 18, 2010
It worked thanks it was really pissin me off
mar

Fitchburg, MA

#62 Dec 19, 2010
Corey wrote:
It worked thanks it was really pissin me off
I know how you felt. Where I live a working rear window defrost is a must have since my car sleeps outside. Glad to hear you got it going.
Brandon

Greenfield, IN

#63 Jan 8, 2011
Just to let everyone know, I found the problem.
Thanks so much Mar for your help.

Originally I posted on here because the rear defrost did not work.
My problem was the purple wire at the back of the HVAC controls. NOT down by the hood release, but yes I did bypass that connector also.

Anyways, wife pulled car over because smoke started coming out of vents. "luckly" After I tore dash apart, wires looked as if they were about the catch fire. So now, any clues how to get a new connector, other than a scrap yard ?

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