Brake lights turn on (and stay on...) in the cold

**MaximusS4** · 01-18-2010 02:28 PM

Hi there,

Its been a while since I've been on the boards and probably an even longer while since I've really driven my S4...

Anyway, back in North America for a bit and the strangest thing started happening last week.

Essentially, I drove form Boston to Montreal and leaving the car outside overnight causes the brake lights to turn on and consequently the battery to drain.

Fiddling around I realized that its as if the pedal gets the opposite of pushed down -- rather pulled up a millimetre or two towards the driver's seat. I only realized that because after the third day of embarrassing jumper-cable adventures to start my car I spent an hour fiddling around with the brakes and light switches. The only way to keep the lights off was to delicately balance one of those snow brushes between the brake pedal and the handbrake (the only 'adjustable' surface in reach. If pressed too hard then the brakes would actually be pressed and the lights would come on and if not pressed enough then the lights alone would turn on.

As I am in Canada and unwilling to drive to Boston with my brake lights constantly on (without my continuously applying 1 mm of force to the brake pedal) I went to a local Audi dealership that was unfortunately unfamiliar with the problem and wanted to charge me a $250 'consultation fee' to try and figure it out. (WTF are they doctors here?)
Additionally, they informed me that the cost of fixing said problem could reach some $3400 --sight unseen-- because "de brake system his de same has de HEY-B-S, hand dey harrr de electronic and would boat ave to be change."

Ummm... so without wanting to sound more disparaging I'm really shouting out to see if anyone "as" any ideas?

Best,
Max

**bez101** · 01-18-2010 02:32 PM

its the break pedal switch remove your lower plastic and u will see it there very cheap and very easy to fit
very comon

**DolphinV8** · 01-18-2010 02:39 PM

If your brake lights come on a few hours after you lock your car, you might have a faulty brake light switch. I will not provide a part number since there seem to be more than one switch, and it's really not that expensive at all. I paid about $11 for it.

Tools needed:
Flat-Head Screw Driver
8mm Socket

Remove the fuse panel cover.

Locate this hole and insert a flat-head screw drive to pop it open.

Remove 3x 8mm bolts to remove the knee bolster.

Remove the data port from the knee bolster and unplug the speaker plug.

Unplug the plug from the footwell light

You will see 2 switches above the brake pedal, and 1 behind it.

This is your brake light switch. Twist it to remove it from the bracket.

Unplug it and install a new switch.

**MaximusS4** · 01-18-2010 02:49 PM

Brilliant!

Thank you so much for your help!

I'll go back there tomorrow...

By chance is there a part number for that sensor/switch that might be helpful when I go see the dealership?

Appreciate it again,
Max

**dextrek** · 01-18-2010 02:53 PM

Interesting, this happened to few couple of times but it went away.
I also noticed when I pull up on the pedal, the light turns off. So I ended up adding more brake fluid and it fixed the problem. However, I didn't check the brake light switch. I'll try that method if it happens again.

**ThirdAudi** · 01-18-2010 03:03 PM

Yes, yes, my wife and I discovered this problem while camping deep in the mountains late one weekend night. Not long after being woken up by some animal walking around outside our tent, the brake lights on our '06 A4 spontaneously turned on casting a red glow onto the wall of our solitude tent. Just a little unnerving!

Went on all night long, needless to say we didn't sleep much!

Turned out to be a faulty brake switch which my Audi dealer replaced for free under warranty.

**DolphinV8** · 01-18-2010 05:02 PM

Originally Posted by dextrek

Interesting, this happened to few couple of times but it went away.
I also noticed when I pull up on the pedal, the light turns off. So I ended up adding more brake fluid and it fixed the problem. However, I didn't check the brake light switch. I'll try that method if it happens again.

The switch might not be universal, so I would recommend calling your local dealership. (I was told that Audi changed the part number 4 times)

**ALWAYS4UDI** · 01-18-2010 06:20 PM

http://www.audizine.com/forum/showthread.php?t=331013

order it from genuine vw audi parts. enter your vin and let them do the work. it'll be cheaper anyways.

**Mr. Corey** · 01-18-2010 08:51 PM

I had this same problem this past fall when temps cooled down, easy fix

**FireTiger91** · 10-20-2012 03:29 PM

[QUOTE=DolphinV8;4806880][b]If your brake lights come on a few hours after you lock your car, you might have a faulty brake light switch. I will not provide a part number since there seem to be more than one switch, and it's really not that expensive at all. I paid about $11 for it.

Tools needed:
Flat-Head Screw Driver
8mm Socket

Remove the fuse panel cover.

I'm new, but this has been a frustrating week with my A4 with this issue...I hope this works. I purchased a genuine switch from the Audi dealer but, what happens when they say you only get one chance? Does it mean you will have no brake light function or can you put the defective one back on until I can buy another one? Do I pull the plunger out, or is it already in this position in the package? A little nervous but it's our family car and I can't keep getting neighbors to jump the car everyday.

Thanks.

**dparm** · 10-20-2012 03:37 PM

Originally Posted by DolphinV8

The switch might not be universal, so I would recommend calling your local dealership. (I was told that Audi changed the part number 4 times)

Probably just revisions to the same part. Easiest way to tell is to look for a letter at the end.

**yObOyGeo** · 10-20-2012 07:13 PM

Happened to me too, twice.. ran to audi bought the brake light pedal switch sensor thingy, it was like 12 bucks. came home, figure id wait til it happens again for me to replace .. almost 2months later and nothing lol

**yObOyGeo** · 10-20-2012 07:14 PM

great DYI tho thabks !

**FireTiger91** · 10-21-2012 06:57 AM

Ok, going to try this right now...i'll let everyone know how it goes:)

**Winners Eat Pho** · 01-02-2013 05:13 PM

Great instructions. The only snag I ran into was user error. I decided to remove the one on the left though the illustration clearly shows with a red arrow the one on the right to remove.

**Goose** · 01-03-2013 01:53 PM

It's drained my battery twice now. My brakes need to be changed, so parts are on order. I've noticed the when it gets cold the brake pedal drops and triggers the switch. I've cut a piece of 2x4 to put underneath the pedal for now. No dead batteries.....