I searched and couldnt find anyone else with this issue. My rear defrost doesnt work, light comes on on the switch, checked voltage at the window, there is about 4.5 volts on both sides?? 03 Cavalier
Should be 12V, and will decline slighty while checking for voltage at different points
- 2004 Cavalier - 124k, owned since new
I know it should be 12, thats why Im confused on what is going on.
One side should be a solid ground.. the other should be 12 volts with the grid turned on, and 0 volts with it turned off. I'd check for the ground first with the grid off... if you have no ground, it won't work.
I was shown this on another forum, it solved the same problem I had: "Just finished the repair of a broken rear window defroster on a 2000 chevy cavalier. Unit would not heat the rear window. I could hear the relay in the dash heater control unit click and the light under the defrost button would turn on and back off after normal time out. I suspected a bad ground, but it turned out to be a burned connector/pin in the +12v feed from the control to the rear. The connector is located under the carpet along the left hand side of the drivers feet area, just below the fuse box and BCM. There is a large (10-12ga) purple wire from the dash control circuit going into the connector and a large black wire leaving. The black wire is bundled with orange electrical tape and runs in the rocker panel along the drivers side back to the rear window grid connector on the drivers side. The passengers side grid connector is the ground connection. There are also some other smaller wires in the same connector (under the carpet). The burned pin in the connector was so bad that I had to build a splice jumper (10ga crimped & soldered) around the bad pins. The other smaller wires and connector pins where fine so I just left them alone. Make sure your repair is strong, there is a lot of current in this circuit and hence the reason why the OEM version failed."
Anyone that would search JBO first would find many, many threads with that same solution... but the OP sounds like a different problem... 4.5 volts is neither 12 or 0....
Sorry it took so long to reply back. Im kinda of electrically dumb at times. I wasnt checking voltage right. So this time, I disconnected one side and measured that to a ground wire, got 12 volts. Unhooked the other side and measured that to a ground wire, 0 volts. So Im getting voltage, but yet the defrost doesnt work. Now from the cars ive worked on in the past, if one line gets a break in it, the others will still work. is this not the case with our cars? Could i have a break in one line and it will take out the whole grid?
No, if one line goes, just the part of the line after the break wont work.
It doesnt make sense, if you have 12V at one side, and 0 on the other it should be working
- 2004 Cavalier - 124k, owned since new
Ha, tell me about it. Im not the greatest with electrical, so I may just have someone look at this for me. Unless someone else has an idea of what to try.
Why don't you have a look at the connector I mentioned in my earlier post. My problem was exactly the same as yours and that was what was wrong. It's an easy fix.
Mine was a burned connector at the control module, the purple one and it was in the harness.
Ryan1
Sorry to bring up an old thread but when you determined the connector pin did you see any scoring to tell you it was burnt out? I have the exact same problem as OP and from what I can see of drivers side harness there is no scoring no black marks anything to show it being burned out.
The sides test 12V and 0V as they should and the ground visually looks ok and the grid is ok from what I can see but cannot test as it is covered by tint but all the lines have no breaks.
