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Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 17155
Experience:  15 years GM master tech
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2006 impala: my rear window defroster not replaced..relay

Customer Question

I am troubleshooting my rear window defroster not working in my 2006 impala. The led light on the knob comes on, i've replaced the relay, and tested the 40amp fuse at bat 3 by exchanging it with the other 40amp fuse. Still now power at the connectors on the windows, tested by connecting leads on my ohm meter to both sides and then by connecting to the purple cable on the window and a ground. really don't know where to look next.
Submitted: 7 years ago.
Category: Chevy
Expert:  Gary replied 7 years ago.
the purple wire at the defroster grid when turned on should be over 12 volts.and the other wire black on the other side of the grid should be ground.when you turn it on put your meter on DC voltage put one lead to the purple and the other to the black wire and see what you have for a voltage reading
Customer: replied 7 years ago.
That is what I have already done and get no voltage reading
Expert:  Gary replied 7 years ago.
ok lets see what we are missing we are either missing the power or the ground.put the meter on OHM'S and one lead on the black wire and the other lead to a good ground and see what you have for an OHM reading.then we can confirm the ground is good and all we have to worry about just missing the power side
Customer: replied 7 years ago.
okay, put on ohm, put one lead on a good ground to the car and the other lead to the black wire, ohm meter reading changed to 0
Expert:  Gary replied 7 years ago.
ok the batt 3 fuse has 12 volts correct?when you turn on the rear defroster?
Customer: replied 7 years ago.
the batt 3 fuse is a 40amp fuse, i have exchanged it with a different 40amp fuse to help troubleshoot but haven't acutally measured voltage. How would I determine if I have 12 volts at the fuse with the rear defroster turned on?
Expert:  Gary replied 7 years ago.
turn on the rear defroster and put your meter on DC voltage put one lead on the fuse opening and the other lead to a GODD ground and see what you have for voltage.make sure you test BOTH fuse openings with it on you should show 12 volts on both sides of the fuse
Customer: replied 7 years ago.
Sorry for my bit of confusion, so I should remove the 40amp fuse at batt 3, turn on the rear defroster, and do the test as you have described?
Expert:  Gary replied 7 years ago.
no if you look at the top of the fuse there are 2 small openings test from those with the fuse in and turn on the should have power at BOTH sides of the fuse with the defroster on and the fuse in place
Customer: replied 7 years ago.
The smaller amp fuses, 25amp and less have the opening you have described, the larger amp fuses are different, they have a plastic color coded cap on the top with no visable place to test.
Expert:  Gary replied 7 years ago.
ok then pull the big fuse and turn on the defroster and see if one of the terminals that connect to the fuse has power.if it does and you know the fuse is good then we precede to the next step
Customer: replied 7 years ago.
11.92 volts on the top leed, 0 volts on the botXXXXX XXXXXd, so it appears we have power at the fuse. And yes I know the fuse is good because I switched it with the other 40amp fuse originally leaving the fuse slot for the other out causing the car not to start, when I replaced it with the original fuse from the batt 3 compartment it started.
Expert:  Gary replied 7 years ago.
ok now what we have is power missing somewhere from that fuse to the back need to find c200 connector in this picture.and find the purple wire in that connector turn on the defroster and see if that purple wire power up when you turn on the defroster.purple wire going into that connector and purple coming out.should be power BOTH side of that purple wire in and out of the connectorgraphic
Customer: replied 7 years ago.
I've looked under the passenger side dash and it appears a good bit of items would need to be removed for allowing me to find where that C200 connecter is. If this is the case then perhaps I've reached a point I am beyond what I need to be messing with and need to bite the bullet and pay the cost to take it into a professional mechanic.
Expert:  Gary replied 7 years ago.
ok.well you made it further than most have to at least try and check all the basics you can at home.but that purple wire is open some where between the fuse and the back glass
Gary and 4 other Chevy Specialists are ready to help you
Customer: replied 7 years ago.
Thank you for your help today, was really hoping for a simple fix, fuse or something, to avoid taking it in, but no such luck on this one. Have a nice day.
Expert:  Gary replied 7 years ago.
you too