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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 29442
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2007 Cobalt SS: My rear defroster..VDC..button lights..relay clicks

Customer Question

My rear defroster on my 2007 Cobalt SS does not work. I have 12 VDC at the fuse and have replaced the relay and it still doesn't work. The button lights up when pressed and the relay clicks but there is no 12 VDC accross the grid. I checked the grid for continuity and it is there so I believe the grid is good. Is there anything else I can try? Thanks.
Submitted: 6 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 6 years ago.

GM Tech (Cam) :

Hello, I'm Cam. Please include all the details about your issue so I can accurately advise you. I cannot see your vehicle so please be detailed.

GM Tech (Cam) :

Where are you putting the ground of your tester?

Customer:

When I check voltage on the fuse I am putting the ground on the strut tower where the GND symbol is.

GM Tech (Cam) :

Does the dash light stay on then showing it is on?

Customer:

Yes and the relay clicks as well.

GM Tech (Cam) :

Ok, one moment while I look up the shcematic.

Customer:

Ok thank you.

GM Tech (Cam) :

OK, you say the REAR DEFOG fuse has no power?

Customer:

If I meter accross the fuse I am reading close to 12V. But when I place my meter accross the grid (+ on one side - on the other) I read no voltage accross the grid.

Customer:

Is that the correct way to meter it?

GM Tech (Cam) :

No, if the fuse is good and you have power to one side, then it is getting power.

GM Tech (Cam) :

Did you test at the rear window?

Customer:

Yes. I also switched to resistance on my meter and ohmed out the grid and there is continuity accross is so I believe the grid is good.

GM Tech (Cam) :

Did you test at one end only to ground?

Customer:

No. I was unable to find a ground at the back window. Would I need to ground to the chassis somehow when checking for voltage at the grid? Maybe I am metering at the grid incorrectly.

GM Tech (Cam) :

What is your meter set on?

Customer:

VDC

GM Tech (Cam) :

Ok, what range?

Customer:

its auto-ranging.

GM Tech (Cam) :

forget that, if you get proper voltage at the fuse then you are testing correctly.

GM Tech (Cam) :

TEst at the wire on one side to the body not the door and see if there is power, No power then find the 16 pin connector in the


Body harness to the headliner harness, in the rear shelf near the LR speaker

GM Tech (Cam) :

You are testing the purple wire.

Customer:

Ok I can try that. And if there is still no power at the grid?

Customer:

The location of the wire harness will be very helpful. I'm glad you were able to tell me where it is.

GM Tech (Cam) :

Work your way back at the simple spots, even try swapping the relay for anther with the same numbers.

GM Tech (Cam) :

just use a different one in the fuse block to swap with .

Customer:

OK. I did buy a new relay at advance auto-parts to see if that would fix it but that didnt do anything. I wasn;t sure which way the relay goes in the socket so i tried it both ways with no luck. Are there any other wire harnesses to check in the defroster circuit or is the one by the LR speaker the only one?

GM Tech (Cam) :

The only connector after the fuse block is that one I showed.

Customer:

Ok. Is there anywhere that I could find the schematic for the circuit? I'm an electronics technician so i have a good understanding of schematics and one would be helpful.

GM Tech (Cam) :

Full Size Image

Customer:

Ok great thank you. Judging by the information I'm giving you do you have any kind of idea what the issue could possibly be?

GM Tech (Cam) :

bad connection somewhere, is my guess.

Customer:

Ok because it just stopped working out of nowhere. The wire harness will be the first area I will check. I suppose something may have come loos.

Customer:

*loose

GM Tech (Cam) :

That is likely, yes.

Customer:

Ok I will check out the connections and see if that solves the issue.

GM Tech (Cam) :

Bookmark this page so you can easily navigate back to it, and so you know, you can reply at any time for follow up information regarding this issue, even after you accept my answer and I will reply.

Customer:

Ok that was going to be my next question if I could follow up with you. That will be great. Thank you for your help..

GM Tech (Cam) :

My pleasure.