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  #1  
Old 15th May 2020, 08:20 AM
Prefferle Prefferle is offline
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Default S8 D3 brake light switch / ABS brakes 00526 - Brake Light Switch Implausible Signal

Hi Folks,

Firstly thanks for being a great forum, truly helpful to us enthusiasts 👍

Regarding my S8, D3 4e 2006:

Recently while moderate braking the abs lamps lit up and when I checked with my VCDS HexNet the fault is:
00526 - Brake Light switch (F)
008 - implausible signal - intermittent.
No other fault codes present except for HVAC heater issues...

My old switch is OEM having the Audi logo and part number: 3B0945511C
I purchased a new switch from febi bilstein 104351 which is listed as a direct replacement (Audi UK parts is still closed here in UK).
I fitted the new switch in accordance with on line guides first pulling out the switch rod fully before fitting and twist locking into position, with the brake pedal remaining in the up position.
I then checked the measuring blocks in VCDS and I can observe the activation of the two switches - the test and light switch contacts changing state when I press the brake pedal - all was well until the test drive and only late in the test drive only after many fine braking operations, when I randomly have the same fault code 00526 occurring again.... I checked the switch fitment as well as verified the two switch contacts changing state - all ok.

Observations:
Looking at Measuring blocks the test contact activates before the light contact. Surely both contacts should activate simultaneously?
I can get only the test contact to activate with a light press of the brake pedal. A firm press will activate both contacts.
If I press the brake pedal lightly the transmission shift lock does not activate, only after a firm press does the shift lock disengage .

Hoping for any guidance you can offer to this. It may be that I have to wait for Audi parts to reopen and purchase an OEM grade part?
Anyone having a wiring drawing so I can check if possibly a corroded or broken wire may be the issue?

Thanks again guys and stay safe

Kind regards
__________________
Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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  #2  
Old 15th May 2020, 09:22 AM
HPsauce HPsauce is offline
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I don't know how a D3 works, but the operation of the switch you describe is EXACTLY how it works on a D2, with a very slight gap between the two circuits.

IIRC, in a D2, one is for the brake lights, the other for the ECU.

I suspect the only real difference between the two switches is that yours is the later design with the automatic setting procedure which you have followed.
The D2 version is adjustable on a screw thread, no automatic/ratchet setting to worry about.
__________________
2003 D2 FL S8. Irish Green Pearl/Beige. Solar sunroof, auto-dim mirrors, electric rear seat functions, ski hatch retrofit; extended leather. Aftermarket DVB-T, reversing camera and full XCarlink (Bluetooth etc.).
2016 Volvo V40 T5 Cross Country (4WD) with ALL the toys including adaptive cruise etc. etc. Osmium Grey with Blonde/Charcoal leather interior. Polestar performance "optimisation". (A much rarer model than a D2 S8 by the way!)
Finally: gone, but not forgotten.....
1998 D2 PF S8. AgateGrey/Platinum. Every option (I think) except electric rear seats, tiptronic steering wheel, ski hatch, towbar & dimming door mirrors.
e.g. Cruise control, NavPlus/TV, Bose, GSM, Xenons, Solar roof, Parking sensors, Alcantara/leather everywhere of course. (internal dimming mirror added later)
1998 (very early) Ford Focus 1.8 Zetec; ABS/TCS, Heated screen/mirrors, Aircon, Auto-dim mirror, Leather, Trip computer, Cruise control, OEM Ford SatNav with CD changer.

Last edited by HPsauce; 15th May 2020 at 09:24 AM.
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  #3  
Old 15th May 2020, 11:10 AM
Prefferle Prefferle is offline
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Quote:
Originally Posted by HPsauce View Post
I don't know how a D3 works, but the operation of the switch you describe is EXACTLY how it works on a D2, with a very slight gap between the two circuits.

IIRC, in a D2, one is for the brake lights, the other for the ECU.

I suspect the only real difference between the two switches is that yours is the later design with the automatic setting procedure which you have followed.
The D2 version is adjustable on a screw thread, no automatic/ratchet setting to worry about.
Thanks HP,

Could you let me know if the switch changes state with the slightest touch of the brake pedal? Or do you get a Slight bit of travel before? Iím already stumped for what this issue can be.
Update: Iíve just metered the old switch and it works electrically fine... it must either be a writing break or something else?... itís an intermittent problem with many miles covered and many applications of braking before the fault is detected. why is it never easy and straightforward with this car😩
__________________
Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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  #4  
Old 15th May 2020, 01:07 PM
HPsauce HPsauce is offline
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Again, on a D2 if it operates with a tiny touch on the brake pedal that's wrong and it causes all sorts of weird problems. You should have to positively press the pedal down a small distance. I can do this without servo assistance though, and indeed with the engine running and brake servo operative it's very difficult to monitor (with VCDS) the transition through the two switches as it's so close.

On a D2 having a "hair trigger" switch really messes with the engine ecu and causes all sorts of odd behaviour. But because the level of electronic management isn't as high as on a D3 there is no error flagged whatsoever, the car just thinks you're dabbing the brakes when actually you aren't. Often it's just a bit of vibration or the pedal not returning fully after you take your foot off!

And just to be clear on the sequence, on a D2 it is possible to trigger the first switch with the ECU thinking the brakes are being applied, but the brakes lights are still OFF.
__________________
2003 D2 FL S8. Irish Green Pearl/Beige. Solar sunroof, auto-dim mirrors, electric rear seat functions, ski hatch retrofit; extended leather. Aftermarket DVB-T, reversing camera and full XCarlink (Bluetooth etc.).
2016 Volvo V40 T5 Cross Country (4WD) with ALL the toys including adaptive cruise etc. etc. Osmium Grey with Blonde/Charcoal leather interior. Polestar performance "optimisation". (A much rarer model than a D2 S8 by the way!)
Finally: gone, but not forgotten.....
1998 D2 PF S8. AgateGrey/Platinum. Every option (I think) except electric rear seats, tiptronic steering wheel, ski hatch, towbar & dimming door mirrors.
e.g. Cruise control, NavPlus/TV, Bose, GSM, Xenons, Solar roof, Parking sensors, Alcantara/leather everywhere of course. (internal dimming mirror added later)
1998 (very early) Ford Focus 1.8 Zetec; ABS/TCS, Heated screen/mirrors, Aircon, Auto-dim mirror, Leather, Trip computer, Cruise control, OEM Ford SatNav with CD changer.

Last edited by HPsauce; 15th May 2020 at 01:10 PM.
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  #5  
Old 15th May 2020, 01:52 PM
Prefferle Prefferle is offline
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Join Date: Apr 2017
Location: Scarborough, North Yorkshire
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Quote:
Originally Posted by HPsauce View Post
I don't know how a D3 works, but the operation of the switch you describe is EXACTLY how it works on a D2, with a very slight gap between the two circuits.

IIRC, in a D2, one is for the brake lights, the other for the ECU.

I suspect the only real difference between the two switches is that yours is the later design with the automatic setting procedure which you have followed.
The D2 version is adjustable on a screw thread, no automatic/ratchet setting to worry about.
Hi HP,

Thanks for those details. The new switch is working as per your description, so must be ok, the controller is detecting an intermittent Issue so possibly wiring or connection issue, it looks to be a bigger challenge to find this problem. Iíll look for wiring and module locations - possibly trace the circuit signals to the controller.

Thanks again, you saved me from buying another switch 👍
__________________
Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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  #6  
Old 15th May 2020, 02:34 PM
MikkiJayne MikkiJayne is offline
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The D2 and C5 A6 will log the same fault in certain conditions, and it puts the ESP on and the engine in reduced power mode when it happens. I've had the issue in both - an incorrectly adjusted switch in the S8, and a faulty switch in the A6. The A6 uses the same ratchet-type switch as the D3.

It might be worth removing the switch, reset the mechanism and reinstall before chasing wiring issues.
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  #7  
Old 15th May 2020, 03:06 PM
Prefferle Prefferle is offline
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Location: Scarborough, North Yorkshire
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Quote:
Originally Posted by MikkiJayne View Post
The D2 and C5 A6 will log the same fault in certain conditions, and it puts the ESP on and the engine in reduced power mode when it happens. I've had the issue in both - an incorrectly adjusted switch in the S8, and a faulty switch in the A6. The A6 uses the same ratchet-type switch as the D3.

It might be worth removing the switch, reset the mechanism and reinstall before chasing wiring issues.
Thanks Mikki, Iíve just completed that. Removed switch, pulled out actuator and then refitted switch. 6-mile test drive all ok until same fault detected again😕. This really looks to be an circuit issue the controller is detecting, with the fault detected at a random time that I press the brake.

What is odd is that I can press the brake many times while driving Over several miles with no issue then the fault would occur with ESP and ABS and sometimes Parking brake failure lights illuminating.

The same fault code every time: 00526 - Brake Light switch (F)
008 - implausible signal - intermittent.

When I reset the fault code all is well again for several miles again, with many braking presses until randomly the fault occurs again... I checked the connector and wiring connectors - all ok. Any other thoughts?

Thanks again,
__________________
Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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  #8  
Old 16th May 2020, 10:35 AM
Prefferle Prefferle is offline
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Join Date: Apr 2017
Location: Scarborough, North Yorkshire
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Quote:
Originally Posted by MikkiJayne View Post
The D2 and C5 A6 will log the same fault in certain conditions, and it puts the ESP on and the engine in reduced power mode when it happens. I've had the issue in both - an incorrectly adjusted switch in the S8, and a faulty switch in the A6. The A6 uses the same ratchet-type switch as the D3.

It might be worth removing the switch, reset the mechanism and reinstall before chasing wiring issues.
Hello again,
so Iíve disconnected ABS Module plug, no corrosion ok, the brake light switch contacts ok. Harness condition looks good, no fraying or signs of damage.
Measuring blocks stable with test contact operating before light switch contact when pressing the brake pedal.
In drive testing I noticed the fault occurs when lifting off the brake. It appears that there may be a relationship between pedal position / electrical switch contact and brake pressure.
some observations when pressing the brake pedal:
Test switch operates at 10.7 Bar.
Brake Light Switch at 15 Bar.
Any chance you have brake pressures (measuring block 009) occurring at the two switching positions?

any additional guidance would be greatly appreciated.
__________________
Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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  #9  
Old 17th May 2020, 12:16 PM
Prefferle Prefferle is offline
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Join Date: Apr 2017
Location: Scarborough, North Yorkshire
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Quote:
Originally Posted by Prefferle View Post
Hello again,
so Iíve disconnected ABS Module plug, no corrosion ok, the brake light switch contacts ok. Harness condition looks good, no fraying or signs of damage.
Measuring blocks stable with test contact operating before light switch contact when pressing the brake pedal.
In drive testing I noticed the fault occurs when lifting off the brake. It appears that there may be a relationship between pedal position / electrical switch contact and brake pressure.
some observations when pressing the brake pedal:
Test switch operates at 10.7 Bar.
Brake Light Switch at 15 Bar.
Any chance you have brake pressures (measuring block 009) occurring at the two switching positions?

any additional guidance would be greatly appreciated.
UPDATE
Decided to:
1. remove ABS wiring harness Wrapping to check for any Internal corrosion or wire insulation damage between ABS plug and wheel arch area.
2. Replace brake light switch AGAIN with OEM grade part.
3. If no improvement - replace ABS module with refurbished warrantied unit.

Iíll update on progress....

Cheers,
__________________
Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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  #10  
Old 18th May 2020, 03:51 PM
Prefferle Prefferle is offline
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Join Date: Apr 2017
Location: Scarborough, North Yorkshire
Posts: 75
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Quote:
Originally Posted by Prefferle View Post
UPDATE
Decided to:
1. remove ABS wiring harness Wrapping to check for any Internal corrosion or wire insulation damage between ABS plug and wheel arch area.
2. Replace brake light switch AGAIN with OEM grade part.
3. If no improvement - replace ABS module with refurbished warrantied unit.

Iíll update on progress....

Cheers,
hello again,
removed inner wheel arch, ABS connector and unwrapped the harness/Loom tape, all wires looking pristine and checked all the way to the rubber boot that takes the harness through the firewall into the cabin.
I also remade the B- terminal to the chassis while I was there.

All wire insulation and ABS plug connections look great. I also got my son to press the brake pedal while monitoring the 12VDC voltage coming through the two brake light switch sets of contacts with no dropout of these signals when I jiggle the harness wires.

im hoping to get another new brake light switch this week (OEM Audi grade this time) and will fit that along with re-taping the wiring harness - then either test again or...

question: Do I now condemn the ABS module and replace with a new-refurbished unit? Any other checks?

looking forward to your thoughts on this.

Thanks guys,
__________________
Present cars
Daily driver: BMW e65 730d
Batmobile: 2006 S8, D3, 4E 5.2L V10 BSM with (loud) Miltek SS exhaust, Carbon Fibre trim, Alcantara headlining, soft close and keyless entry.
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