OK, I noticed a problem about ~3 weeks ago (maybe more, maybe less) when I had the rear window defroster on.............I tried adjusting my driver's seat (power seat) and nothing happened.........it wouldn't move forward, back, up or down........so I was like WTF?? I got home and checked the fuse panel (suspecting a blown fuse) and smelled something almost like burning insulation (again, WTF?? ).

Anyway, I found out that the rear defroster and the power seat work off the same circuit breaker --- not fuse --- circuit breaker (which is a small metal box, about 3 times the size of a regular fuse). It was hot to the touch (I burned my finger on it ) so I just left it for a while. After a few minutes, I tried the seat again, and it was working. I tried the rear defroster, and it was working too, so since then I haven't used the two devices simultaneously (hoping to avoid the same problem).

HOWEVER, yesterday when I left for work, I turned the defroster on, and in less than 2 minutes, it shut off, and the back window was nowhere near cleared! I tried turning it back on, but all I heard was the "click" of the relay somewhere, but the indicator light never came on, nor did the defroster. Just for fun, I tried the seat, and sure enough, it wouldn't move.

SO, I left the defroster alone after that, but tried it once last night, and once again this morning, and each time, it only runs for about a minute or two (instead of ~5 minutes like usual) and leaves my window just as frosty as when I first turn it on. Could the circuit breaker be defective?? Or is there a problem with the rear defroster shorting out somewhere?? Has anyone else had this problem??..................I'm taking the car into the dealership tomorrow, but I just thought I'd ask first incase anyone has had this happen, and as well, just to let others know of the potential problem with using the defroster and power seats at the same time (and since the defroster is very necessary here in the Great White North, this is a problem for me).

 

1 of 2 things, circuit breaker over load. Replace with a 30 amp fuse. Or my problem, the rear glass had to much resistance.

The glass had to be replaced. I hope it's still under warranty.

This is happening to a few of us. So don't feel alone.

 

Yeah, it's still under warranty..............I only bought it on June 26th of this year. Hopefully they can figure it out, and don't just tell me to live with it! (they'd better not?! ).

The other thing that has bothered me about this since I first had the problem, is that rear defrosters draw a lot of current on their own, so why would they have doubled-up the circuit for the defroster with a power seat?? (which I'm sure also draws quite a lot of current? ) ...........it seems like a bad engineering decision IMO.

 

Bad engineering decision? BAD ENGINEERING DECISION???

Surely not! Surely GM wouldn't do something like THAT!!!

Some GM bean-counter bucking for a promotion to to Head Dipsh*t figured out that by including one less circuit breaker in your car, GM could save $XXXXX in production costs. THAT'S the reason for the decision.

Try out the higher-capacity fuse. That should be the first thing to check.

 

I had a 1994 GMC Sonoma and that is what happened to my power door locks.......they quit working and when I checked the fuse (circuit breaker) it was so hot it put a blister on my finger. I took it to GMC dealer and they said that where a wire was running through my door jam to control my power windows and door locks ,had a bare spot causing a short and making the breaker get hot. It could be a short in the wiring or a bad breaker.

 

That's exactly what I've been fearing as a potential problem ...........a short in a wire could be very difficult to find. Hopefully it is simpy that the breaker is faulty, but since SteveMat has been having a related problem, I think there's something more to it.

Until now, I've had zero problems with the car, but this one really p!$$es me off....................especially since it's something that appears to be a very common problem.

 

I have a similar problem with mine. However if I touch the brake pedal, the rear defroster/seat starts working again..

 

i had the same problem also, but mines started only when i FIXED the rear defogger. My defogger worked just fine except for one strip down the middle which didn't work, i bought one of them repair kits, and was on my way, one humid night i turned it on to clear my windshield... turned off after about 60 sec's, check the circuit breaker, scorching hot! pulled out my multimeter, and found a whole ohm load of resistance on the strips. So i got a razor blade and cut the strip that i repaired... been working fine ever since. except for the patch of windshield that stays foggy which anoys the f**k outta me everytime i glance back there. i also heard that gm is having a problem with the rearwindshield having too much resistance, cuasing this problem. my problem is my 5 years are up on warrenty, and im am not gonna pay for replacement of a new windshield!

 

OK, so I took the car to the dealership today. When I went to pick it up, I was told "you can take it for now, but I'll call you soon to arrange bringing it back to replace the rear glass". Well, "probably" the guy said. I guess there's too much resistance through the wires in the back, so they're gonna change the whole glass!? So "Dimoncutr", same problem as your's (and likely others too ).

The thing that bugged me though, is that when I picked it up, I got in and found my seat adjusted --- fine, I know they were working on it --- but, in all their "diagnosing", they disabled the power seat now, so I went back in to see if they could do anything about it, and the guy said most of the mechanics had left by that point (~4:30pm) so I'm going back in the morning so that they can at least make my driver's seat work until they fix the "big" problem. So that's where it's at!

I'll keep everyone posted on any more info / changes I find out tomorrow. (and sorry to anyone who has to replace the window if it's out of warranty................while the guy didn't know the exact price, he figures around ~1200 for the back glass!!).

 

If the rear window had "too much resistance" then the oppisite effect would occur. There would be too little current flow to heat up the glass. A heater circuit is a balance between the available potential and the resistance needed to create heat to melt snow and ice.
The window may have too little resistance therby creating greater current draw and throwing the circuit protection which in this case is a circuit breaker. A glass with too much resistance would have a different symptom.

First off you need to know what the circuit is actually drawing. With all of the components that are hooked up to it operating at the same time. 30 amps is one of the bigger circuits. I would seriously doubt that the rear window defogger is drawing more than 30 amps. That sounds like a hell of a lot. In order to heat up the glass, it has to be a high resistance circuit through the grid. There have been instances of bad circuit breakers on F-Cars in this circuit specifically.

My diagnosis would start off with some way to determine how much current was actually flowing in the circuit and then through the individual branches of the circuit. I.E. You have to rule out the breaker before everything else because it is easiest thing to replace.

 

Dave:

You're probably right on the too much/too little resistance thing.........electronics isn't my strong point. Also, I'm going on the word of the service manager, and he's not the mechanic either! Since it is under warranty, I don't really care (nor do I know how) to begin diagnosing the problem myself.

In regards to whether it's the circuit breaker or not, apparently they put a new one in just in case, but I guess it didn't make a difference.

Oh, and I got the seat fixed this morning......................somebody didn't plug it back in properly.

So now I have to wait patiently (and with a foggy back window ) 'til the new year when they can talk to the GM Tech guys and determine for sure that it's the back window. Yay.

 

Same thing happens here Other night I was cruisin with some girls in the back (fist time havin anyone in the back) and I had to move my seat up, so I did. Laterthat night after they were out I tried to move it back but it wouldn't. Couldn't figure out what was wrong either... But then about 10 min later it worked again. But yeah, since you mentioned all this, I realized that the rear defrost was onwhen it wasnt workin, and it shut off when i WAS finally working. Hmmm, I'm having too many probs with GM electronics

Nate

 

That sucks that you're having the problem too, but my question is, what do you need a rear defroster in Florida for?! ......................I thought the temperature never goes below ~70 degrees anyways?!

I still can't believe that the "solution" to the problem is replacing the whole rear glass............that is f'n ridiculous!

 

Oh yeah, I neglected to mention I'm home on leave right now, here in South Dakota. Florida is where I'm stationed at in the Navy. But yeah, here in Sioux Falls it's been below freezing quite frequently. Hehe, sorry about that.

Nate

 

about 2 months ago I was drag racing at the track, and the rear defroster just quit working. I think I might have made a pass with it turned on (normally I turn all stuff like that off) and I think that might have cooked it somehow. my power seat still works fine, but nothing happens when i press the rear defroster button. Now I just don't use the rear window if there's ice on it. I wonder if only a part of that metal circuit breaker can fail... If so maybe I need a anew circuit breaker. Someday I guess I'll take it to the dealership. I have a 6 year warranty. (And I intend to screw as many parts out of them as I can in those six years).