Brake light saga continues I NEED HELP PLEASE

xxxmike · May 9, 2017

So i have been on and off looking at my brake light issue. The joys of sometimes working a 7 day week!
I've had the rear lights out and checked all the bulbs but they are all good. I have not changed them for wrong ones or anything silly like that.
The brake lights stay on all the time.
If i remove fuse number 23 then they go out.
I have changed the switch for a genuine VW part, but that didnt work.

I have stripped the wiring back from the switch (these are on the master cylinder) as far into the firewall/bulkhead as i can go and there is no damage to any of the 4 wires.
One is a power wire and one is earth and the other 2 i image are for the rear lights???
I am fully lost now as to where to go next and really need some help.

I am seriously thinking of just throwing this junk heap into a dealer or getting an auto electrician out.

Any ideas???

thanks

RUM4MO · May 10, 2017

Have u managed to work out how that switch actually works, or operates, maybe by reconnecting the old one you might manage to work out how it works by manipulating it when it is not fitted. It might help if you have a small magnet and or a bit of ferro magnetic steel, as I could almost image that there will be a area in the master cylinder plunger/rod that is either magnetic or not and that switch is a hall sensor device?

What happens when you leave the switch connector unplugged?

If all that is wrong or proves nothing, maybe you will find that the brake lights get switched on by the BCM in response to a changed condition being generated by that switch, so it would be a faulty BCM?

Guessing, I'm afraid, sorry.

xxxmike · May 10, 2017

Seems to be some sort of sensor or magnet on the bottom that picks up on movement in the master cylinder. There are no moving parts. It's better it's up underneath and stays there with the bolt and the plug goes into it.
There is power going TO the plug constantly with the ignition on but I'm not sure if that's meant to be or not. Only a small 0.9v though. That's from the black and red pin I think?

My other thought was a faulty BCM.

If the switch is unplugged the brake lights stay on which makes sense if it's a fail open circuit.

If I disconnect the rear lights the high level brake light stays on too.

I've purchased another genuine switch in case the previous one I got was faulty or damaged. For £15 I thought it's worth a shot.

If it's a BCM do I need a genuine new one or can you reprogram second hand ones.
Thanks.

PeterA · May 10, 2017

The switch may switch a negative hence why you're only seeing .9v,the next step is to work out if the rear lights switch positve or negative because this will make a difference as to what will be causing your issue.One check to do is disconnect the bcm,the brake switch and all the back lights,this will give you a loom which shouldn't give any results from testing,this way you can eliminate any shorts.And as a side point if you're working on a modern car don't use an old fashioned bulb test light as probing the wrong wire can fry stuff !,a led test light or multimeter are best.

xxxmike · May 10, 2017

Thanks Peter, i have a pretty good multimeter thankfully.
Do you know of a wiring diagram for the BCM? What wire is what? I have not looked at the BCM yet, is it behind the fuse panel?

thanks

PeterA · May 10, 2017

Sorry Mike i don't have any specific info on the bcm,i used to be a basic car sparks hence the little bit of info

RUM4MO · May 10, 2017

Roughly speaking, the BCM is below the steering wheel zone, but behind the panel. Yes you can reprogram a used BCM but, the easiest way to do this is to scan that car using VCDS for instance, hopefully that will also tell you something about what is wrong with that car. You would use the coding found by scanning that car to if necessary alter the coding of the used one you buy - but, what if that BCM has that same problem or another?

Locate your nearest VCDS owner and take it from there?

Edit:- I am on holiday right now but when I get back home at the weekend, I have a broken front spring to sort out on the late 2009 Ibiza, while doing that I'll have time to unplug the brake light switch and report back what happens.

xxxmike · May 13, 2017

had a full scan this afternoon with the VCDS (or whatever its called) software.
On the first full scan i got this-

Address 01: Engine Labels: 03C-906-024-BXW.lbl
Part No SW: 03C 906 024 BK HW: 03C 906 024 BK
Component: BXW MM4HV 4119
Revision: --H11--- Serial number:
Coding: 0000071
Shop #: WSC 06402 785 00200
VCID: 68D81F32581E200141-5178

1 Fault Found:
16955 - Brake Switch (F)
P0571 - 000 - Implausible Signal - MIL ON
Freeze Frame:
Fault Status: 01100000
Fault Priority: 2
Fault Frequency: 1
Reset counter: 179
Mileage: 125971 km
Time Indication: 0
Date: 2011.10.01
Time: 00:14:48

Freeze Frame:
Bin. Bits: 00000000
Load: 0.0 %
Lambda: 0.0 %
Speed: 0.0 km/h
Temperature: 28.0°C
Absolute Pres.: 1009.8 mbar
RPM: 0 /min
Readiness: 0000 0101

-------------------------------------------------------------------------------

Address 03: ABS Brakes (J104) Labels: 6R0-907-37x-ABS82.clb
Part No SW: 6R0 907 379 AB HW: 6R0 907 379 AB
Component: ABS8.2 front H03 0001
Revision: --------
Coding: 100200DB006F00B9082D00E800D300000000
Shop #: WSC 04941 000 00000
VCID: 7EF4596AED9A8EB19B-802A

3 Faults Found:
01314 - Engine Control Module
004 - No Signal/Communication - Intermittent
Freeze Frame:
Fault Status: 00100100
Fault Priority: 0
Fault Frequency: 3
Reset counter: 219
Mileage: 0 km
Time Indication: 0

Freeze Frame:
Hex Value: 0x0005
Hex Value: 0x0000
Hex Value: 0x0083
Hex Value: 0x139C
Hex Value: 0x00FF
Hex Value: 0x007F
Hex Value: 0x7E00
Hex Value: 0x0000

01312 - Powertrain Data Bus
004 - No Signal/Communication - Intermittent
Freeze Frame:
Fault Status: 00100100
Fault Priority: 0
Fault Frequency: 3
Reset counter: 219
Mileage: 0 km
Time Indication: 0

00474 - Control Module for Immobilizer
004 - No Signal/Communication - Intermittent
Freeze Frame:
Fault Status: 00100100
Fault Priority: 0
Fault Frequency: 3
Reset counter: 219
Mileage: 0 km
Time Indication: 0

-------------------------------------------------------------------------------

Address 09: Cent. Elect. (J519) Labels: 6R0-937-08x-09.clb
Part No SW: 6R0 937 087 D HW: 6R0 937 087 D
Component: BCM PQ25 H+4 H46 0207
Revision: BF046001 Serial number: 0147 046100346
Coding: 24882BE888610100003000007E0B1CC80040400F608C0000200000000000
Shop #: WSC 64564 324 38760
VCID: 3E74996AA91A4EB1DB-806A
01758 - Bulbs for Brake Lamps
006 - Short to Plus - Intermittent
Freeze Frame:
Fault Status: 00100110
Fault Priority: 2
Fault Frequency: 254
Reset counter: 221
Mileage: 126036 km
Time Indication: 0
Date: 2011.10.02
Time: 20:56:57

01758 - Bulbs for Brake Lamps
011 - Open Circuit - Intermittent
Freeze Frame:
Fault Status: 00100110
Fault Priority: 2
Fault Frequency: 254
Reset counter: 221
Mileage: 126036 km
Time Indication: 0
Date: 2011.10.02
Time: 20:56:57

00532 - Supply Voltage B+
011 - Open Circuit - Intermittent
Freeze Frame:
Fault Status: 00101011
Fault Priority: 2
Fault Frequency: 3
Reset counter: 219
Time Indication: 0

-------------------------------------------------------------------------------

xxxmike · May 13, 2017

Then ran a second after clearing the faults and no faults were logged and all the warning lights disappeared from the dash but the brake lights remained on.

RUM4MO · May 14, 2017

That is a nuisance, but I think that it confirms that the brake light switch is working okay.

So, I'm thinking, without having an experience of this exact fault, that the BCM is faulty and is holding the brake lights on, while not in itself having a failure mode that is not showing up on the onboard diagnostics system, that is annoying but can happen.

One thing though, now you know the coding of the current J519 - ie the BCM, and its part number, so that should make sourcing a used one a bit easier.

RUM4MO · Sep 25, 2017

xxxmike, did you ever get to the bottom of this problem, if so what was the final fix?

RUM4MO · Oct 27, 2017

RUM4MO said:
xxxmike, did you ever get to the bottom of this problem, if so what was the final fix?

Well, you asked the questions, what was the final outcome of this?

xxxmike · Oct 27, 2017

Hiya.
Sorry for the late reply. It’s been an absolute nightmare.
Spoke to seat many times about this and after sending my ecu to a friend of a friend who doesn’t normally do vag work but did his time he managed to fix it.
It was a signal issue from the switch under the bonnet on the master cylinder to the ecu. The wiring was fine but the ecu was seeing it as an open circuit so kept the brake lights on. I’ve not idea what he actually did but it was an issue with the ecu.
For anyone unlucky enough to get his issue it’s best off just sending your ecu off to an ecu specialist to fix.
Glad it’s all over with now and will be sold

RUM4MO · Oct 27, 2017

Thank you very much for your prompt reply, maybe that will answer a few questions for people with the "brake lights stuck on" issue!

xxxmike · Oct 27, 2017

I changed the bulbs first then the brake switch with genuine parts twice and then started working on the wiring before getting to the ecu being the issue. Painful job but hey ho

RUM4MO · Oct 28, 2017

Sound logic and starting with the cheaper parts first, so as time moves on, I wonder if this was a one off or will quite a few others end up with this basic problem being either wiring or ECU.

Bit of a nuisance, for a long as VW Group used crappy brake pedal switches that had a design revision every few years, it was always, I think , the switch and never the ECU, so now they have cured the switch issue, which peanuts to replace, and ended up with potentially bigger or expensive potential problems.

Maybe this will only happen to a few Fabia/Polo/Ibiza but it is good to have other's experiences as reference to what/where the problem might lie.

jimcon · Jul 6, 2018

Oh feck.. . I've just had my brake lights staying on. Just changed the switch.

Took it into a local vw garage and they think it's a wiring fault...

.. If it's the ecu... Feck.

jimcon · Jul 6, 2018

Fixed it.

With a hammer .

I had the old switch.... Disconnected the new, plugged it in... Lights on

Got a magnet and put it in the switch.... Lights off. Magnet off...lights on.

Aha... Something is in the master cylinder that moves to the switch.. Magnetic that causes it to activate and turns on the lights.

Small hammer .. Few taps to the master cylinder casing near the switch and problem solved .

Lights now working normally :thumbup:

RUM4MO · Jul 7, 2018

That is a nuisance, I thought that there was a bigger maybe 2 part repair kit that needs fitting, ie a new switch and a new ??? - maybe to allow this switch to be closer to or further away from the where it was originally. So it sounds a bit like a slight design dimensional error that can cause a few people this problem - good that you solved it though!

RUM4MO · Jan 20, 2019

Bumped for someone with this issue!

Brake light saga continues I NEED HELP PLEASE

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