Rear Defrost not working.....any suggestions [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: Rear Defrost not working.....any suggestions


Ricky81
11-13-2009, 12:33 AM
Hello......noticed the issue this morning......rear glass frosted up and turned on the rear defroster.......light stayed on.....but nothing was happening.....checked the side mirror and was warm....but nothing was happening to the rear window......still frozen and showed no signs that it was working.....I used the search but found little info....not to much info on this issue.....on a thread it said something about a bad ground.......Can anyone help me out.....or point me to the right direction on where to start.....thanks....Ricky:undecided

vball61
11-13-2009, 01:08 PM
I had the same thing happen to me a couple of days ago. I wiggled the connectors on both sides of the glass, and the next time I tried it, it worked. Go figure.

Does your rear wiper still work? If not, check the 30A fuse 3 (labeled LGM #2) in the rear fuse block.
Touch the defrost grid with a test light connected to a good ground. It should light up when defrost is operating. If it doesn't (make sure you try a few spots) then there's an issue with the power supplied by the liftgate module.
Ground for the defrost grid is shared by the license plate lamps, liftgate module, left taillamp, and chmsl... If those don't work either, check the ring terminal attached to the lower left side of the liftgate opening, under trim.
The wires which pass from the body to the liftgate through the grommet/sleeve at the top of the liftgate opening have been known to break/chafe over time, so that's a good place to look as well.

Good luck.

Ricky81
11-13-2009, 10:46 PM
thanks for the response...the day this happend I wiggled the connectors on the rear windsheild .the licence plate lights are on and the wiper blades is working......took the vehicle in at the shop...and checked the wirings.....the mechanic told me it must be a bad ground or a loose wire somewhere.......:undecided

macmic87
11-15-2009, 10:52 AM
first thing i would do is check for voltage with the system turned on. if there is voltage check continuity of the heater grid with the wires removed. there could be a break in the circuit or a weak mounting tab. that's my 2 cents.

kickinkz
12-08-2009, 10:02 AM
I've got kind of the same problem...Only I have 3-4 lines working, the others aren't....I'm guessing my grid is toast...there's no visible damage to the grid from what I see....

Phil

ieatglue
12-08-2009, 11:11 AM
I've got kind of the same problem...Only I have 3-4 lines working, the others aren't....I'm guessing my grid is toast...there's no visible damage to the grid from what I see....

Phil

:iagree:

I have 2 lines that don't work. The rest work fine :undecided

the roadie
12-08-2009, 11:46 AM
It's the kind of problem than be troubleshot (if not cured) in 5 minutes with a meter in the hands of somebody who knows how to use it. Or not solved at all in hours of guessing and experimentation in the absence of a meter. Test lights can do half the job - checking for voltage. But only a meter can test for resistance or continuity with the power turned off.

CSDenali
12-23-2009, 08:19 PM
Roadie,

Same issue here. Only the top half of the defrost grid works. I have a meter, but am pretty rusty. Will you provide a brief instruction for testing?

Still also battling an intermittent power failure to the driver's door module. (The door switch asm) The power turns on and off at will. I pulled the switch assembly and verified all harness connections were tight. Afterward, the frequency of the "on/off" game slowed up. However, it is still present. Power source? Ground?

Thanks. :hail:

the roadie
12-24-2009, 01:50 PM
Think of a defrost wire as a painted-on heater wire just like what's in a toaster, except flat. There are two power tabs, one on each side of the window, and the power spreads out to each wire in parallel. Parallel means all of them have the same voltage (12V) at one end where they come together at the tab, and ground at the other end.

If the painted-on wire is intact, and continuous from side to side, there's 12V at one and and 0V at the other. And 6V in the middle. 3V at the 1/4 way distance. 9V at the 3/4 way distance. The voltage you see with a meter (if you poke through the painted-on insulation with a needle or pin to get to the copper underneath.

A painted-on wire with a break in it will have 12V on one side of the gap, and 1/4" away on the other side of the gap, will have 0V. By inspection and moving the place you look for voltage with your needle, you can discover where the gap is.

I found this drawing in a search, and although the author confuses current and voltage, it shows the idea.

http://i.ehow.com/images/GlobalPhoto/Articles/2118507/rearwindowdefroster_Full.jpg

CSDenali
12-24-2009, 02:46 PM
Thank you. Happy Holidays!

MichEnvoyBoy
01-02-2010, 10:14 AM
Hmmm... thinking about it, my rear defroster hasnt had anything but 1 line working since I bought it in 2004 :hissy: Mine has always worked like this (the red line being the only line that works):
http://i49.tinypic.com/2n71qmq.jpg

The connectors to the defroster grid are on, but I cannot see any other reason for just 1 line of the grid working besides the grid just being bad. I mean, if the wires were loose, bad ground, etc.. wouldnt it not work at all?

Anyways, I called a local junkyard and was prepared to buy a back glass out of another t360. Has anybody ever replaced the rear glass?

flrdr
01-16-2010, 05:55 PM
I have one grid line that is not working. It appears that the problem is where the line attaches to the 12v vertical supply line. I cannot get to the connection as it is covered with a black coating (paint??). Would it be possible to simply connect this bad grid line to one of the adjacant lines using a repair kit? Would this pull too much current through the "good" grid line? Ideas? Thanks

the roadie
01-16-2010, 05:59 PM
You can try scraping the paint off the vertical distribution bus. For the short part where you have two lines being fed by one narrow line, that section will have double the current and could overheat and die, yes. Good to worry about. Then you'd have two dead lines, potentially worse then today.

flrdr
01-16-2010, 06:12 PM
Thanks for the advice Roadie. I may just leave well enough alone. I'm afraid that I may damage the main bus by scraping off the paint. One line really isn't a big deal. :thx

EME
01-26-2010, 08:55 AM
A couple months ago I too started having a problem where my mirrors would heat but my rear window barely did or not at all. Last night I metered the connections and they were registering anywhere between 0 and 3 volts. I took the door panel off, started wiggling wires and my meter jumped to 13v...yea! Everything seemed firmly seated so I traced the defrost wires to figure out which harness was the problem and on closer inspection, I found that the power contact had turned blue and the socket was slightly melted! Hmmmm....a Ford in Chevy's clothing?

Ricky81
01-26-2010, 06:03 PM
A couple months ago I too started having a problem where my mirrors would heat but my rear window barely did or not at all. Last night I metered the connections and they were registering anywhere between 0 and 3 volts. I took the door panel off, started wiggling wires and my meter jumped to 13v...yea! Everything seemed firmly seated so I traced the defrost wires to figure out which harness was the problem and on closer inspection, I found that the power contact had turned blue and the socket was slightly melted! Hmmmm....a Ford in Chevy's clothing?

Good to know EME....still haven't fixed it but when it gets warmer I'm gonna look into it......

JRad
01-26-2010, 10:36 PM
Good to know EME....still haven't fixed it but when it gets warmer I'm gonna look into it......

But when it gets warmer, you won't need it :dielaugh:

Same trouble here.

EME
01-27-2010, 04:04 PM
Now I've just got to find me a new connector.

vball61
01-28-2010, 01:05 PM
Now I've just got to find me a new connector.

Here are the rear defrost connector part numbers:
1-way black connector to each side of the defrost grid: 12092133
4-way black connector into the liftgate module: 12052856

Both of these connectors can be purchased at mouser.com...

EME
01-28-2010, 02:51 PM
Here are the rear defrost connector part numbers:
1-way black connector to each side of the defrost grid: 12092133
4-way black connector into the liftgate module: 12052856

Both of these connectors can be purchased at mouser.com...

Sweet! Thanks!

the roadie
01-28-2010, 03:00 PM
Here are the rear defrost connector part numbers:
1-way black connector to each side of the defrost grid: 12092133
4-way black connector into the liftgate module: 12052856

Both of these connectors can be purchased at mouser.com...I never knew they had those! Cool! Are those including the contacts, or do you have to buy them under a different part number?

vball61
01-29-2010, 02:15 PM
I never knew they had those! Cool! Are those including the contacts, or do you have to buy them under a different part number?

I don't believe the terminals are included - only the plastic connector.

If you click the 'Data Sheet' link under the part description on the Mouser site, it'll take you to the Delphi Connectors website. There, if you select the 'Related Parts' tab, it'll show you all of the terminals and other components (CPAs, TPAs, seals, mating connectors, etc.) which work with that part.

Unfortunately, Mouser carries a 'mixed bag' of GM connector parts. The only terminal they sell which is correct for our defrost circuit (tin plated, 2.0mm^2 gage wire) is the replacement for the 4-way connector: p/n 12066214.
The correct terminal for the 1-way at either side of the glass is p/n 12034109, but Mouser doesn't appear to stock it at this time.