Park Avenue rear defrost not work

RKWOODY

MEMBER
1999 BUICK PARK AVENUE
3.8L
6 CYL
TURBO
FWD
AUTOMATIC
285,000 MILES

I replied to another thread on my issue but will also ask the question separately.

I am still having issues with my '99 PA rear defrost. I have replaced antenna module and have power all the way across the grid but it still won't work. (In face my rear glass was just replaced due to a crack so I know the grid is fine) I stopped in my local GM garage and talked to service tech Bob (who is 67 yrs. Old and has been working on cars since he was 12!) Who had originally diagnosed problem as faulty module. When I explained that I tested the grid he asked if the grids tested the same all the way across. As you move further from the electrical source. I told him that my test light was equally bright all the way across, top to bottom. He said if that is the case I then have a ground problem because the light should get dimmer as you test and move further from the electric source. I'm not an EE so I wasn't sure what to make of this. Bob said I need to check the ground for the grid but I don't know where that is. I'm perplexed - I now I have power, the back window is brand new and the antenna module if fine. Any insights would be GREATLY appreciated - thanks in advance!

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Tiny

5 Replies

WRENCHTECH

MECHANIC
20,757 POSTS

Sounds like he may be correct. Any circuit requires a complete circuit of both power and ground and can't operate without both. You have 2 wires attached to the grid. One is power and one is ground.
This circuit grounds through the radio antenna module coil

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Saturday, December 13th, 2014 AT 7:50 AM

WRENCHTECH

MECHANIC
20,757 POSTS

This is the antenna module coil

https://www.2carpros.com/images/external/79033092.gif

REMOVAL PROCEDURE

Remove the right sail panel trim.
Disconnect the body harness from the module.
Remove the bolt (2).
Disengage the tab on the module (1) from the slot in the sail panel.

INSTALLATION PROCEDURE

Engage the module tab in the slot.
Align the module hole for the bolt (2). Rotate downward the module (1).

NOTE: Refer to Fastener Notice in Cautions and Notices.

Install the bolt (2) for the antenna ground coil module.

Tighten
Tighten the bolt to 7.5 N.m (66 lb in) .

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Saturday, December 13th, 2014 AT 7:57 AM

RKWOODY

MEMBER
6 POSTS

Interesting that I actually pulled that small module off yesterday. Would you replace it or try to repair it? I've never seen them go bad from discussions I've read in various forums. Have you seen these go bad with other folks? I may order anyway - cheap part; less than $10.

Thank you very much for the prompt response!

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Saturday, December 13th, 2014 AT 8:33 AM

WRENCHTECH

MECHANIC
20,757 POSTS

We don't make repair decisions based on what we may have seen in the past. We simply, systematically test the circuit. It's a pretty basic thing to test for ground on that wire without guessing.

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Saturday, December 13th, 2014 AT 8:36 AM

RKWOODY

MEMBER
6 POSTS

So would you suggest I bypass the module and ground the wire coming off the grid using another wire; and the re-test the electrical current going through the grid. To see if it decreases as you move across the grid?

Thanks again