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Discussion Starter · #1 · (Edited)
I posted the following in an Audi forum but got no response...thought i'd try here before I break down and take it to a shop.
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I'll try to keep this as brief as possible.

2008 Audi S4 Avant, 96,000 miles, no accidents, no major issues

- right rear brake light bulb goes out, according to sensor
- remove r.r. Lamp module, replace bulb, even though it looks OK.
- reinstall
- all lamps in module, including back up light, are now out with sensors indicating same on dash display
- remove lamp module again, carefully inspect
- wires from grommet to multipin plug appear fine, no wear or bare areas or insulation cracking that I can see...jiggling/bending wires made no difference
- both contacts (multipin plug and receptacle on lamp module) have slight brown discoloring around the brown wire (hot?) pins (heating due to corrosion?)
- used very fine file to clean contacts
- reassembled module
- worked fine for 2 days, then r.r. brake light and r.r. turn signal bulb sensors activated...neither of bulbs would light
- removed lamp module, cut hot wire from multiple plug, fed it through small hole in plastic module lamp chassis and soldered it directly to the hot side of the metal chassis on the module.
- tested before reassembly and all bulbs worked, no sensors triggered
- reinstalled module
- r.r. bulb sensor and r.r. turn signal sensor came on again
- removed lamp module again, checked solder joint (I cannot pull it loose) switched bulbs around, cleaned contacts on bulbs
- all bulbs work, just none work in brake light socket
- gave up and settled for just having turn signal and reinstalled everything
- everything worked!
- just went out to use car and r.r. brake light and r.r. turn signal show bad again
- pulled out of driveway to go to store and within a block, all errors cleared and turn signal cycled normally
- before I got to store, r.r. brake light bulb sensor came on but signal still worked
- came out of store, now r.r. brake light and r.r. turn signal are out again

I know if I take it to Audi they're just going to yank the entire wiring harness for that side and replace the whole lamp module and charge an arm and a leg.

Before I do that, is there ANYTHING that I've overlooked with this?

NOTE...since writing the above, I've removed it again. I've cleaned and abraded all mating surfaces of bulbs and sockets and tightened the clamping prongs that hold the bulbs. It worked fine on installing it and it was out again the next morning. A big heavy hammer is working its way into my thoughts. Note that there are no wires inside the lamp module itself, it's all just sheet metal circuits. I'll try to find a picture.
 

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Discussion Starter · #2 ·

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First off, you're right, stay out of the dealership. They're gonna hang ya! (Over and over again) Better off to struggle on your own, as miserable as it is. Back track the circuits and look for a splice or ground that could be corroded. Also, when it's acting up, perform a "wiggle test" to try and isolate the suspect area of loom. Unfortunately when electrical isn't acting up, it's impossible to diagnose. Keep at it man, you'll get it. Sorry I don't have more.
 

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Do a full scan with VCDS/VAG-Com and see what comes up

Lots of modern shit with CAN controlled lights and circuits can be a total fucking nightmare. And often any fault...can be so obscure and far removed from what you think...that it will never be found by conventional means.

Although checking all bulbs fitted are correct and in good order and all connections/wiring are sound are fairly universal.
 

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I work on shit like this for a living. Without any wiring diagrams handy it sounds to me like the lamp driver module is going out. Which is probably the entire body control module on that car. Sounds to me like you have done your diligence on the lamps circuits in the rear. You will at least need to take it to someone that can scan and confirm the module is going out by properly checking the wires from the module to the rear lights. If your car does need a module it will most likely need to be programmed by the dealer in most cases.
 

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You know what's a bummer, you Google this kind of stuff and 300 people with the same car have the same problem, lol.
My wife's Trailblazer had tail light failures, even the new and improved housing wouldn't last, you think the cop that
pulled her over for tail light out cared if it was a constant problem, lol
 

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I work on shit like this for a living. Without any wiring diagrams handy it sounds to me like the lamp driver module is going out. Which is probably the entire body control module on that car. Sounds to me like you have done your diligence on the lamps circuits in the rear. You will at least need to take it to someone that can scan and confirm the module is going out by properly checking the wires from the module to the rear lights. If your car does need a module it will most likely need to be programmed by the dealer in most cases.
Anyone with VAG-Com/VCDS would be able to program the module.

It isnt cheap to buy...but at the same time if you do work at your own vehicles and own VW's or Audi's it would be well worth buying as it isnt horrifically expensive.

https://store.ross-tech.com/shop/cat/vcds/

http://wiki.ross-tech.com/wiki/index.php/Diagnostic_Procedures#Audi
 
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