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Rear defrost and heated mirrors not working

Tiny
RJC42005
  • MEMBER
  • 2000 BUICK PARK AVENUE
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 72,000 MILES
I have already checked the 40 amp fuse under the hood nothing is wrong with it. I have check the relay (it broke while attempting to take it out) in the rear seat area and installed a new one. I have also checked the antenna module and connecting harnesses and they are not melted or burned (but purchased a new one just in case). The grid is intact as well. Only thing I've noticed is the defrost button on climate control module (in dashboard) isn't lit up, but it beeps when pressed. This is my son's first car and need it to be 100% functionally safe.

What am I missing?
Any and all help is greatly appreciated!
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Saturday, December 19th, 2020 AT 1:02 PM

29 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
Hi,

If the light isn't turning on, either there is no connection at the grid or the switch is bad. I did find a few technical service bulletins related to grid connector tab failure and how to repair it.

Do me a favor. Check where the grid plugs in and confirm the tab isn't damaged. Also, I want you to take a test light and check to see if power makes it to the grid. If you look at pic 1, it shows what happens to the grid connection.

If you find the test light does turn on, then there is a connection issue at the grid. If it doesn't turn on, move to the switch, and confirm there is power both to it and out from it. If there is power in and not out, replace the switch.

I attached two more pics showing the entire wiring schematic for the rear defroster. I had to cut the pic in half to make it readable. It shows a purple wire going to the defroster so make sure it has power. Also, I realize you checked the 40 amp fuse. Make sure power is both in and out from it and also check the 10 amp fuse highlighted in pic 2.

Here are a couple links you may find helpful:

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find.

Joe

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Sunday, December 20th, 2020 AT 10:08 PM
Tiny
RJC42005
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Okay. It'll take a day or so. I have to go buy a test light. So the 1st link, is that the fuse box under the hood or in the back seat that you want me to test?
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Monday, December 21st, 2020 AT 1:24 AM
Tiny
RJC42005
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  • 18 POSTS
Also, forgot to mention, that when I press the defrost button on dashboard, I do not hear a clicking sound as I've seen in a video or two on the internet. I pressed it while simultaneously feeling and listening for it to engage, but heard nothing and felt nothing. Sorry I maybe should've mentioned that as well. I'm a DIY'er. Please forgive me.
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Monday, December 21st, 2020 AT 1:53 AM
Tiny
RJC42005
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  • 18 POSTS
Which kind do I use? I have the pen looking one, or do I need the one that looks like a screwdriver?
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Monday, December 21st, 2020 AT 5:09 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Honestly, either will work. Since you won't use it too often, the one on the right will be much less expensive.

The 40 amp fuse is in the under hood fuse box and the smaller one is behind the glove box in the vehicle.

You may want to check the relay in the trunk fuse panel. Here is a link that shows how that is done:

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

If there is another relay with the same part number, switch them to see if it makes a difference.

Let me know. Also, you can use a multimeter or voltmeter if you have one.

Take care,
Joe
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Monday, December 21st, 2020 AT 7:35 PM
Tiny
RJC42005
  • MEMBER
  • 18 POSTS
Okay, test light completed. Defrost/antenna module changed (as shown in picture, new one one the wall, old one in hand). Climate control panel in dashboard changed new one on bottom). All fuses and relays changed (new one pointing at located underneath rear seat). I press the rear defrost button even on the new climate control panel, and still no illumination on button, and still no rear defrost. Wth am I not seeing or missing?
FYI: all parts were ordered before posting on this site looking for help.
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Sunday, December 27th, 2020 AT 2:40 PM
Tiny
RJC42005
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  • 18 POSTS
As before when I press the rear defrost button, it isn't lit up but does beep (like the original one). And while pressing it I listen for a sound while touching the relay (the new one in the back seat) and feel nothing or hear nothing.
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Sunday, December 27th, 2020 AT 3:15 PM
Tiny
JACOBANDNICKOLAS
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If you have someone test for power at the grid when you press the button, is there power?

Let me know.
Joe
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Sunday, December 27th, 2020 AT 8:54 PM
Tiny
RJC42005
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There is power up to (via the test light) harness that goes into the antenna/defrost module, new antenna/defrost module, then little harness on top that leads to grid tabs, then to grid. No brakes, burns. Grid lines are intact as well.
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Monday, December 28th, 2020 AT 12:54 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Has the switch been replaced? If you have power to the grid and then it goes out, it sounds like the switch can't handle the load.

Let me know.

Joe
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Monday, December 28th, 2020 AT 10:55 PM
Tiny
RJC42005
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It's an entirely new (refurbished) system.
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Tuesday, December 29th, 2020 AT 12:36 AM
Tiny
RJC42005
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  • 18 POSTS
Climate control panel new: but has same issue as the old one.

Relays: new

Antenna module: new
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Tuesday, December 29th, 2020 AT 12:38 AM
Tiny
RJC42005
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  • 18 POSTS
Can't say the grid has power. I assume if it did the the defrost would be working correct? I do know that there is power up to the harness that plugs into the antenna module (via test light and new antenna module). The small harness on top of that that plugs in and goes to grid tabs is in good shape as well and the tabs are not damaged or broke.
The only thing that I haven't tested is the harness that plugs into the new/refurbished climate control panel (in dashboard) because well, it does power up the unit but has the same problem as the old one I took out (rear defrost button isn't lit up but does beep). Other than that the only thing I can tell (and I don't know if it's supposed to or not supposed to) is that the rear relay (which is new) located in back seat while pressing the defrost button while touching the relay and listening. Does not make a clicking sound nor do I feel the relay engage when button is pressed. Other than these 2 things (only going off YouTube video's I have found/watched) I don't know what else to search for (and I don't know if the relay is supposed to do this for particular vehicles or all vehicles).
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Tuesday, December 29th, 2020 AT 3:09 AM
Tiny
JACOBANDNICKOLAS
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If there is power, the only other thing can be ground or an open in the grid itself. By checking if there is power back to the grid, that would tell me if it is after the plug.

When you check power to the module, is it plugged in? We could simply have a weak connection that is failing when a load is placed on it. Also, I know you checked the 40 amp fuse. However, did you check the 10 amp one behind the glove box that I mentioned?

Let me know.

Joe
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Tuesday, December 29th, 2020 AT 10:34 PM
Tiny
RJC42005
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I will plug the harness into the module and light check to see (while plugged in) if the power goes beyond the module to the upper harness that connects to the grid. The grid is intact, no broken lines or missing portions. And yes, I did check all the fuses and relays including the 10amp under the glovebox, all are either new or not blown. When I get home today I will check that harness while it's plugged into the module, and let you know.
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Wednesday, December 30th, 2020 AT 3:53 AM
Tiny
JACOBANDNICKOLAS
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Hi,

Sounds good. The idea that you hear a beep when you turn it on could indicate a short at some point.

Let me know.

Joe
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Wednesday, December 30th, 2020 AT 10:44 PM
Tiny
RJC42005
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A short in both units though?
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Thursday, December 31st, 2020 AT 1:04 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
Honestly, it's unlikely but possible. Something is preventing operation.

Let me know.
Joe
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Thursday, December 31st, 2020 AT 10:12 AM
Tiny
RJC42005
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I'll check after work with the antenna module/harness to see if power goes beyond to the grid. After that I just don't know. And you mentioned something about a ground? I'd need info on how to find that and what to look for.
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Thursday, December 31st, 2020 AT 10:16 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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I'm looking through different schematics that seem to be conflicting. At the grid, are there one or two wires? I believe there should be only one, but I'm seeing two different things.
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Thursday, December 31st, 2020 AT 11:17 AM

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