[urq] Brake System Failure Warning

[Maurits Jonkergouw]

Thanks Bill,


The bottom switch would close if the pressure drops below the minimum of 36 bar, so you're 
questioning is correct.
This means the switch is not a sensor, and therefor can be checked with test wires and a 
DMM.

And the latter is exactly what confuses me: tests done with the DMM indicates the switch 
does not close for hours. If I connect the bottom 'real' connector only, it triggers the 
warning after 5 minutes. So to verify if it's really the switch that closes after 5 
minutes and not a faulty wire, I need to connect both the real connector AND my DMM and 
see what's what.


Regards,
Maurits


----- Original Message ----- 
From: "Wbremer" <wbremer at maine.rr.com>
To: "'Maurits Jonkergouw'" <urquattro at moregraphics.nl>
Sent: Sunday, June 13, 2010 4:43 AM
Subject: RE: [urq] Brake System Failure Warning


Maurits:

I question whether either switch would close (and complete the warning
circuit) only when the bomb has lost all pressure or the hydraulic pump has
(totally failed and lost all pressure.



-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf
Of Maurits Jonkergouw
Sent: Saturday, June 12, 2010 2:20 PM
To: Audifans
Subject: [urq] Brake System Failure Warning

Hi guys, this time I really don't how to fix this "challenge" lol.


Challenge:
'Fake' Brake System Failure warnings (voice and idiot light).

Checked:
A. black/purple connector behind the radio > it was already disconnected.
B. wires+connectors brake switch > tested OK with dummy switches.
C. warning switches (bottom) and (side) > tested OK with dummy wires and
multimeter.


My understanding of the warning system and those switches is this: the side
switch will 'close' if the brake accumulator (bomb) would completely lose
pressure and the bottom switch will 'close' if the hydraulic pump fails with
running engine. Otherwise, both switches are in the 'open' position with
running engine only?

To verify the switches, I hooked up dummy wires and a DMM to each switch and
test drive the car > both switches stay 'open'.

To verify the wires/connectors, I hooked up 2 dummy switches and test drive
the car > manual switch 'open' : no voice warning > manual switch 'close' :
voice warning and idiot light.


Conclusion:
I 'faked' the behavior of the switches/connectors and they are working fine
during testing, but if I connect the 'real' connectors, the voice warning is
triggered after approx. 5 or more minutes of driving...

Question:
How is this physical possible? I presume the switches are simple 'on/off'
switches and not 'sensors' like like the oil pressure warning sensor?
I also noticed the bottom switch does sweat a little bit and perhaps the
connector is filled up with hydraulic fluid after 5 minutes, 'shorting' the
connector as if it was closed?

I appreciate your help as always...

Regards,
Maurits

1986 quattro GV (rebuilt)
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