Go Back   AudiWorld Forums > Audi Models > Audi A8 / S8 > A8 / S8 (D2 Platform) Discussion
Sign in using an external account
Register Forgot Password?


A8 / S8 (D2 Platform) Discussion Discussion forum for the D2 Audi A8 and S8 produced from 1994-2002

Reply
 
 
 
 
LinkBack Thread Tools Search this Thread Display Modes
Old 01-17-2011, 02:53 AM   #1
A 8
AudiWorld Member
Account #: 63552
 
Join Date: Oct 2003
Posts: 114
Default Break pressure switch failure -ABS problem

Hi all, hoping for some help.

I randomly get the ABS warning light when I start the car. I took it to a non authorized Audi mechanic who read the fault code and it said that the break pressure switch or its curcuit failed.
It took some time for them to decide exactly what the break pressure switch was but they concluded it was the switch that senses if you hit the break pedal, it's the same that turns on the break lights. They changed it but it did not help. I dismantled the old switch, 2 poles and concluded it cant be the right switch.

Anyone else have this problem or know where the "break pressure switch" is located?

Thanks/
__________________
2010 A8 FSI 4.2 Quattro, Nightvision, Adaptive Cruise Control, Sport, 20" 10 parallel design 265/40R 20, Nav plus incl DVB and DAB 3G with hotspot, Comfort 4 zone. Phantom Black with Pearl effect.
A 8 is offline   Reply With Quote
Old 01-17-2011, 08:09 AM   #2
AudiWorld Super User
Account #: 184138
 
silverd2's Avatar
 
Join Date: May 2010
Location: East TN
Posts: 2,260
Default

There is no brake pressure switch in your car. That is an older type brake light switch, not used in Audi's anymore. A true brake pressure switch is usually screwed into the master cylinder, a sealed hydraulic switch used on earlier VW's and Audi's.

You DO have a 2 function mechanical switch at the brake pedal..brake lights and brake position sensor, which sort of detects pressure by how far brake is pushed in (position).

You obviously need to get to a "qualified" independent mechanic (or dealer if necessary), to get qualified diagnosis...read codes, inspect obvious components (including the proper installation of brake pedal switch and communication with that switch by ABS computer), etc. ABS light could be caused by a dirty or failing wheel speed sensor at any of the 4 wheels or even an electrical problem at the ABS hydraulic unit under the hood. I would start with unplugging and reseating the the big plug on that unit...then checking for dirt/grease build up at the wheel sensors. If you go to a dealer, DO NOT be talked into replacing the hydraulic unit..they do NOT go bad and cost huge $$....but the electric module on the side of that unit can fail and can be repaired at a reasonable price by places like modulemaster online...a good indy mechanic knows this and can take care of it.
__________________
Not a "guru" (whatever that means), but I did stay in a Holiday Inn Express last night.

Mine: '01 A8 SWB
Hers: '03 Allroad 2.7T
Dog's: '90 Passat wagon
silverd2 is offline   Reply With Quote
Old 01-17-2011, 09:17 AM   #3
AudiWorld Super User
Account #: 80919
 
tozoM8's Avatar
 
Join Date: Sep 2004
Posts: 6,621
Default

I bet your mechanic pulled this code. http://www.audipages.com/Tech_Articl...itcherror.html
__________________
'05 Porsche Cayenne Turbo titanium on black
'01 black on black allroad 2.7T
'01 black on black A4 1.8T 5MT
----------------------------------------------------------------------
'01 black on black twin turbo S8 6 speed manual(euro TDI 6th gear), RNS-E, Passport SRX SOLD
tozoM8 is offline   Reply With Quote
Old 01-17-2011, 10:32 AM   #4
A 8
AudiWorld Member
Account #: 63552
 
Join Date: Oct 2003
Posts: 114
Default

Thanks, good info!

The mechanic pulled the code when it was active and I have used an authorized mechanic on this issue before and they pulled the same fault. I have also checked the break switch install myself including soldering the cables to the connectors just to make sure...no difference. Typically I get the problem when the car has been sitting in a damp environment for a while. It goes away after a night in my warm(ish)garage or after an hour of driving. I always need to restart to clear the fault so its not a condition that gets checked continously.

If it was the abs sensors I assume the fault codes would indicate just that so I am thinking the problem must be at the other end of this curcuit, do you know if that is at the ABS hydraulic unit or is there another control unit I need to look for?

I know the hydraulic units electrical connectors was a problem on older models but mine has the "newer" version with the connector mounted vertically.
__________________
2010 A8 FSI 4.2 Quattro, Nightvision, Adaptive Cruise Control, Sport, 20" 10 parallel design 265/40R 20, Nav plus incl DVB and DAB 3G with hotspot, Comfort 4 zone. Phantom Black with Pearl effect.
A 8 is offline   Reply With Quote
Old 01-17-2011, 03:24 PM   #5
AudiWorld Super User
Account #: 184138
 
silverd2's Avatar
 
Join Date: May 2010
Location: East TN
Posts: 2,260
Default

Diagrams seem to show that brake light switch portion of pedal switch goes dierctly to light control module (relay)(1.5mm wire red w/black, terminal 2 on switch) and the pedal position sensor portion goes directly to the ECM (.35mm wire white w/red term 4).
Terminal 1: 1.5mm red w/white from fuse to brake light.
Terminal 3: .35mm black w/yellow from fuse to pedal position.
__________________
Not a "guru" (whatever that means), but I did stay in a Holiday Inn Express last night.

Mine: '01 A8 SWB
Hers: '03 Allroad 2.7T
Dog's: '90 Passat wagon
silverd2 is offline   Reply With Quote
Old 01-18-2011, 02:16 AM   #6
A 8
AudiWorld Member
Account #: 63552
 
Join Date: Oct 2003
Posts: 114
Default

Good info again, I will open the ecu box and maybe reseat the connector.
Thanks/
Michael
__________________
2010 A8 FSI 4.2 Quattro, Nightvision, Adaptive Cruise Control, Sport, 20" 10 parallel design 265/40R 20, Nav plus incl DVB and DAB 3G with hotspot, Comfort 4 zone. Phantom Black with Pearl effect.
A 8 is offline   Reply With Quote
Old 01-18-2011, 02:16 AM
AudiWorld
Audi R8




Paid Advertisement
 
 
 
Reply

Tags
2005, a8, abs, audi, brake, breaks, buy, failure, forum, pedal, position, pressure, problems, s4, sensor, switch, yelow


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On



Join AudiWorld

All times are GMT -8. The time now is 08:24 PM.


Copyright 2014 AudiWorld.com Audi Enthusiast Community