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Help with brake lights!!!

  #1  
Old 01-09-2011, 10:57 AM
1st Gear
Thread Starter
Join Date: Feb 2009
Posts: 19
Default Help with brake lights!!!



Dear Colleagues,

Happy New Year to All. I am reaching out to all the experts with an issue I have been experiencing with my 2005 4.2 A8L. Cutting straight to the point, my brake lights will come on when I park outside ONLY at night in cold temperature. I noticed this issue last winter (happened a couple of times) and when I depressed the brakes the brake lights will go out.

At the time I thought it was perhaps the EBP activating because I may have been parked on uneven (elevated) surface. However, the situation has gotten much worse this winter, and the strange thing is that “this ONLY happens when it’s COLD and at NIGHT”. When I park outside during the day, the brake lights DO NOT turn on, but when dark falls – It lights as if I had my foot on the brakes.

I have also noticed a few clicking sounds when the brakes are depressed, but I am unsure what this might be.

I have NO WARNING lights indicating a problem; so I’m not sure how to even tackle this problem. I am not an expert when it comes to mechanics, but I can change my own oil on the A8, do a brakes and roto changes, replace spark plugs and little things like that.

Any ideas on where to start with this problem will be much appreciated. It’s just annoying to walk out at night and have your brake lights lit bright RED. “

My neighbor thought I was once trying to commit suicide, and actually call me in the middle of the night; because her daughter noticed my brake lights had been on for 5-HOURS, and she wasn’t sure if anyone was in the car, so she told her mother to call me! ---- Funny at the time but becoming annoying!
 
  #2  
Old 01-09-2011, 01:13 PM
2nd Gear
Join Date: Jun 2010
Posts: 624
Default

My theory: Brake light switch at the pedal is faulty...and apparently more prone to sticking on when frozen (or mechanism contracting more when cold)...possibly got a little moisture in it from melting snow off your feet.
Just a guess, but fits perfectly with what you described.
 
  #3  
Old 01-09-2011, 01:21 PM
1st Gear
Join Date: Sep 2010
Location: Peabody, MA
Posts: 32
Default Check Grounds

It looks like the only way the that both sets of brake lights would come on would be a failure of the Comfort System Central Control Module (Behind Battery). I would start by checking the ground, (brown wire) located under the passenger seat. Have you had any other problems with the exterior lighting, ie. turn signals. Also if the high mount brake light is illuminated with the other brake lights, the module i mentioned above, and the brake pedal switch are the only things they have in common, if it is not illuminated I would look into the grounds (brown wire) for each of the tail lamp assembly. Less likley, due to the fact that it is 2 seperate grounds and the tail lamp control module still require a B+ sig to change states. It looks like the CSCC module only controls exterior lighting in the rear part of the car and only gets its signals via CAN connection, I don't think your problem is in the CAN (you would have far greater issues). Concerning the pedal switch, when you depress the pedal the lights go out, or when you depress and release, the lights go out, if so do they stay out. Check it out let me know. BTW this is my first attempt to troubleshoot on this forum and am using Mitchell drawings. If I am missing something please lit me know.
 

Last edited by Torsion'sA8; 01-09-2011 at 01:36 PM. Reason: More info (Pedal Switch)
  #4  
Old 01-09-2011, 06:02 PM
2nd Gear
Join Date: Jun 2010
Posts: 624
Default

Originally Posted by Torsion'sA8 View Post
It looks like the only way the that both sets of brake lights would come on would be a failure of the Comfort System Central Control Module (Behind Battery). I would start by checking the ground, (brown wire) located under the passenger seat. Have you had any other problems with the exterior lighting, ie. turn signals. Also if the high mount brake light is illuminated with the other brake lights, the module i mentioned above, and the brake pedal switch are the only things they have in common, if it is not illuminated I would look into the grounds (brown wire) for each of the tail lamp assembly. Less likley, due to the fact that it is 2 seperate grounds and the tail lamp control module still require a B+ sig to change states. It looks like the CSCC module only controls exterior lighting in the rear part of the car and only gets its signals via CAN connection, I don't think your problem is in the CAN (you would have far greater issues). Concerning the pedal switch, when you depress the pedal the lights go out, or when you depress and release, the lights go out, if so do they stay out. Check it out let me know. BTW this is my first attempt to troubleshoot on this forum and am using Mitchell drawings. If I am missing something please lit me know.
Well, you're ahead of me with info available...I have nothing on D3's. The "Night Only" thing is puzzling to me. In a D2, the only systems that are light sensitive are rear views, instrument lighting and the climate control (sensor on top of dash), to my knowledge.
Do D3's have other systems that recognize light and dark?
 
  #5  
Old 01-09-2011, 06:09 PM
1st Gear
Join Date: Sep 2010
Location: Peabody, MA
Posts: 32
Default Sorry I was wrong

It didn't make since to me that the brake light signal would be going through the CAN. It isn't, after looking at the drawing again your brake light signal goes strait to the module that controls your brake lights. The signal goes to harness B pin 20 (red/black) next time you catch your lights on grab a digital multi meter or a circuit safe test light and see if you have B+ at pin 20. Your CAN connection is on the same harness (orange/green and orange/brown) so I would be a little uneasy about unplugging it to test because I am not sure if it would throw a code, maybe someone else could answer that. But long one short, it could be your brake light switch. I suppose it could get cold enough to shrink an already weak spring allowing the contacts to complete the circuit, or like silver said could me moisture from snow. Let me know if this helps.

Looks like you could also try pulling fuse #12 on the left hand side of your dash, looks like it only powers the B+ going brake light swich, that looks like a quick and easy way to tell if the brake swich is where the fault is.
 

Last edited by Torsion'sA8; 01-09-2011 at 06:20 PM. Reason: More info (Fuse)
  #6  
Old 01-09-2011, 06:14 PM
1st Gear
Join Date: Sep 2010
Location: Peabody, MA
Posts: 32
Default No Idea

I am not sure, I did a quick search for photocell and light sensor, all i got was daytime running lights, dimming rear view and cluster illumination.
 
  #7  
Old 01-09-2011, 08:16 PM
2nd Gear
Join Date: Jun 2010
Posts: 624
Default

I wonder if the "night only" is just a coincidental correlation with temperature drop? ...and has nothing to do with actual lighting conditions?
 
  #8  
Old 01-09-2011, 08:19 PM
1st Gear
Join Date: Sep 2010
Location: Peabody, MA
Posts: 32
Default Yep

That is what i was thinking, today we had a high around 40 low of 17 tonight
 
  #9  
Old 01-09-2011, 11:22 PM
1st Gear
Thread Starter
Join Date: Feb 2009
Posts: 19
Default

Thanks to everyone that weighed in on this issue, and the wonderful feedback. As inquired by TORSION'S A8, the high brake light "inside the car behind rear seats" illuminate, in addition to the rear "outside brake lights"

When the car sits in the cold at night, and all THREE lights come-on, I usually depress the brake pedal which turns off "high brake light and both exterior brake lights. NO ADDITIONAL LIGHTS ARE OUT; whether inside or outside.

Thank you!
 
  #10  
Old 11-21-2011, 01:55 AM
1st Gear
Join Date: Nov 2011
Posts: 3
Default

Originally Posted by kwathom1 View Post
Thanks to everyone that weighed in on this issue, and the wonderful feedback. As inquired by TORSION'S A8, the high brake light "inside the car behind rear seats" illuminate, in addition to the rear "outside brake lights"

When the car sits in the cold at night, and all THREE lights come-on, I usually depress the brake pedal which turns off "high brake light and both exterior brake lights. NO ADDITIONAL LIGHTS ARE OUT; whether inside or outside.

Thank you!
Hello kwathom1. I am in exactly the same situation with your brake light coming on situation during the start of winter. I had it at the start of last winter which i survived, but last weekend i was not that lucky. On saturday morning i noticed that the brake lights are on, but managed to drive 20 odd kms on sunday. Monday morning the car wont start as the battery is completely drained.

Can you guide me how you fixed your situation? I have a 2006 Audi A4.

Pavi
 

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