1998 Buick Park Avenue rear window de-icer

Hello Ed,

I just recently repaired my 2000 Park Ave. With the same problem. I purchased a GM OEM C-Platform Service Manual that covers most Park Ave's of the '97-'05 vintage. The service manual was a little confusing but I'll guide you through the steps.

First question is: Have you noticed a loss of AM/FM radio signal strength or a lot more noise just recently? The reason I ask will be explained as we step through the troubleshooting process. Seems GM designed the grid on the rear window for two purposes in our beloved Park Ave's. One is as a window defogger and the other is as an AM/FM Antenna.

If you haven't had any discernable loss of radio signals, the first thing to check is the 40A fuse labelled RRDEFOG located in the engine compartment, under the hood just behind the battery and to the left of the FUSE RELAY CENTER box. It's labelled FUSES. There are two snap retainer clips on the end of the cover. Carefully pry them away and pull the cover off. Inside the cover is a legend/layout showing where fuses are located. Look for the 40A RRDEFOG fuse, I think it's yellow. You can test it for continuity by using a DMM and probing the two exposed end points. With the DMM set on the low ohms scale you should read very close to zero. If zero, that means the fuse is good. If you want to be absolutely certain, you can pull the fuse out and probe the two legs. If you pull it out and it's bad, you'll know it just by looking at it.

The next point to test is located under the back seat. To remove the seat, push back on the lowest point of the front of the seat while pulling it up until you feel it release. There are two catches about 18 inches in from the doors under the seat that the seat latches to. Once released, lift it up and allow the two back catches to drop out from their retainers that hold the back of the seat in position. Remove the seat from the car.

Located close to the center on the floor you will see a black box with a star shaped spinner nut holding the cover on it. I think it's labelled FUSE RELAY BLOCK. Loosen the nut and remove the cover. Once again on the inside of the cover you will see a legend/layout of the fuses and relays. The relay you are looking for is labelled as HTD BK LITE, should be Number 1 and is the largest one of the group. Mine was made by Siemens. A quick test to see if the relay is functioning is to activate it via the dashboard control button with the ignition switch on, radio off, car not running and doors closed. Let everything settle out once you turn on the ignition swich before activating the control button. You will be able to hear a clicking sound as you activate/deactivate the control button. You can actually feel it, if you can reach back and touch it while turning the control switch on and off.

If the HD BK Lite relay, aka DEFOGGER relay, seems to be functioning the next step is to check for voltage feeding the DEFOGGER grid. To get to this test point you have to remove the Sail Panel (trim panel covering the drivers side of the rear window). To remove it, I started by pulling the slender part of the trim over the rear door out. It's retained by plastic tongues going into pressure clips. Pull it straight out so you don't break the panel or crack the tongues. The end of this this portion dovetails into a joint at the junction over the center post between the doors on the drivers side. Once this section is free, work your way back carefully prying and pulling. The main portion where the seat belt comes through is held in by press in plastic screws, which can be pryed out with caution. Once these are free you will have to pull the main sail portion up and forward as it has an interlocking leg that engages the back deck to keep the bottom in place. Once free, carefully work it down the seat belt and push it out of the way. You should now have access to the connections for the DEFOGGER grid.

There should be a black plastic module known as the Radio Antenna Module exposed with a two white wire connector and a coaxial antenna cable plugged in on one side and a two wire (black and white) connector plugged in on the other. The single connector side of the module should have the black and white wires going to the grid on the rear window. The white wire is for the antenna signals and the black wire is for the 12 VDC power to the DEFOGGER grid. With the ignition on and the dashboard control button activated, you should read between 11-13 volts on the DMM probing the black wire as positive connected to the grid and the DMM common lead to the car's chassis ground. If not, disconnect the two white wire connector on the other side of the module and probe the lower side of the connector, the side with the retainer, do not probe inside the module. You should read 11-13 VDC there. If not, the HTD BK Lite/DEFOGGER relay is bad, even though it's clicking, the contacts may be misaligned or pitted.

If you observe voltage on the lower side of the input connector but don't see it when you probe the black wire connected to the grid, reconnect the input connector and remove the output connector (the two wire black & white one) and probe the lower contact "inside" the RADIO ANTENNA MODULE. If you observe voltage there, then the RADIO ANTENNA MODULE is good. Look very carefully at the black wire going into the back side of the output connector to the grid and give it a good tug. There are signs and indications that GM may have had a bad rash of these connectors installed in vehicles where the crimps on these wires ended up on the insulation instead of nice bright copper strands and over time corrosion sets in and results in the defoggers not working.

If you found corrosion in this connector, there are replacements available for $4-$5 that can easily be cut and crimped in. I would also check all other connectors and crimped connections because crimped connections that have insulation under them created high resistance joints that cause more current to flow and create heat that melt and weaken other wires and connectors in the circuit. Check it all out thoroughly.

If your radio reception went bad at the same time that the DEFOGGER started to malfunction, I would suspect the RADIO ANTENNA MODULE and would have recommend you replace it but a wire connection is easier to repair/replace than a module.

Please let me know how you make out and I hope that this helps others with the same problem.

Backyard_Jim

Thanks Backyard_Jim,

Your write up was very clear and thorough. I think it has helped me to find my repair.

Pics of the 2 wire connector going into the Radio Antenna Module here:

https://www.2carpros.com/articles/mitchell1eautorepair-car-repair-manuals

Thanks Backyard Jim. I followed your very informative suggestions to the relay by the back window. There I found the wires going into the bottom of the relay (the side with the coaxial) to be toast. The connecter is melted and the relay itself also looks like it got very hot in 1 area. Any ideas?

Hello Bruce,

Sounds like you've experienced the same thing several of us have. I'm beginning to wonder if this isn't a fire source for Buicks. I'll have to check the NHTSA statistics and see where it leads.

In response to your question, the integrity of the relay module may have been compromised but it is probably still functional. If it's severely distorted, I would highly recommend replacing it as the solder connection of the lug on the pc board where the connector plugs into may have melted and resolidified as a cold solder joint, which would create the same problem all over again, a high resistance joint that would create heat and eventual failure again, not to mention a possible car fire.

Just to test the functionality of the antenna and defrosting grids, you could cut the wire back, strip and redress it, then install a new connector on and reconnect it, but clean up the lug on the pc board by scraping it to get rid of corrosion, oxidation or residues from the previous melt down first.

Once reconnected, the radio should pick up stations more clearly than before and you should be able to turn the defroster on and measure the proper voltage on the connector leads. If you know how to use an ammeter, you could test for current draw, once you've verified there's voltage to the defrost grid. After you make the connector repair, initiate the defrost cycle at the controls console, which is on a timer and let it cycle, watch for the power on indicator for it to go out, then feel for heat on the outside of the module. If too hot to touch, disconnect the power to it and get another module because it's bad or been compromised. Also, if it stays stone cold, it's probably bad too! You'll have to make your best educated guess.

Replacing electrical and electronic parts can be a very expensive venture, especially if your not familiar with a devices function. Never hesitate to ask that "dumb question" because messing with electrical equipment is not only costly but can be very dangerous, even at low voltages. Better to learn something safely than learn a lesson the hard way. There are a lot of good mechanics and electricians out there willing to help. Glad you asked.

Please be careful and good luck with your repair.

Backyard_Jim

Great site and detailed answer. 98 Park Avenue 115K here. I had been smelling like hot wires for some weeks and finally the rear defogger went out, tried the fuses, no go, then followed your directions and found the Radio Antenna Module. The lower wires are scorched looking, I managed to yank them out and the plastic clip is half melted/burnt off and the RAM unit looks like the area where it was plugged in may have melted? There is a noticeable circle around that area visible from the outside at least, and with the burnt wires I'm assuming the RAM unit is toast, even though I was getting a current from the wire. Any ideas? Winter is almost here and seeing out the back window is a plus. I think I'm lucky the darn thing didn't burn down! Thanks.

A quick update. I did indeed have a bad RAM unit! It was black and fried on the inside, darn lucky it didn't start a fire. It had even scorched the side leading to the window and the antenna (as well as the other side of the unit) which were hard to see at first. Had to cut and strip all the wires back, and splice them with the butt end splices. Careful with that heat gun on the splices, it can scorch your interior!

Defogger is working great now! Haven't put the trim back on yet, making sure it continues to work before I pack it all back in. Cost me about 100 bucks, had to order 2 ACDelco PT1183 Female 2-Way Wire Connector with Leads as both sides were scorched, look carefully.

I'm not very mechanical at all, though electronic stuff I'm fairly comfortable with and it's really not a difficult repair, thanks to the information I found on this site. Thanks everyone!

I sorry to bring up an old post, but I have been having the same problem with my 2000 Park Ave. For a long time. Just now getting around to fixing it. I found my module melted also. I called GM to try to see if there were any call backs or at least if they have improved the module, but they didn't seem to know about it. Sort of hard to believe since there are so many problems. Even found one in the junk yard that was melted. Probably if each person had complained to GM, they would be forced to give some compensation or come up with a better solution to the problem. Just makes me want to ask every owner I see with a Park Ave. If their defrost works

Backyard Jim -

Great detailed info but I'm 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!