[s-cars] A Different Brake Light Question

Tom Green TRGreen at comcast.net
Sun Jun 28 17:31:02 PDT 2009


  I would assume you get from 0 to 2 pumps before the pedal is hard  
after the
car sits?  If it takes 30 pumps to deplete the accumulator pressure  
shortly after
shutdown, then the pump must be supplying pretty good pressure to charge
the accumulator that well.  Then, pressure is bleeding off during the  
period the
car sits.  Have you tried to quantify this time period?  I.e., does  
the system
maintain enough pressure so the brake light is out at restart for 1  
4 hours?  Or, does this brake light not correlate with lack of boost  

When the brake light is on continuously when hot, can you deplete the  
assist pressure by pumping the brakes and get a hard pedal while  
If so, then you have a  problem.  If the brakes and steering operate  
maybe it is a sensor problem.  The sensor of interest is on the brake  

You did not mention fluid appearance or changes but with the work done
on the system, I have to assume it is fairly new.  It does need to be  
clean to
perform up to specs, and all the banto bolt screens need to be clean  
as well
as the filter screen in the reservoir neck.  The filter screen is  
bright metal, not
black.  That comes from the hoses and pump seals and can severely  
flow and pressure in the system.

Are there any hydraulic fluid leaks?  Even the smallest seep will  
deplete the
stored pressure as well as make a mess where you can't see new problems.


> -----Original Message-----
> Date: Sat, 27 Jun 2009 14:15:58 -0400
> From: "Fred Munro" <munrof at sympatico.ca>
> Subject: Re: [s-cars] A Different Brake Light Question
> To: "'Douglas Fifield'" <douglas.fifield at gmail.com>,	"'Scarlist'"
> 	<s-car-list at audifans.com>
> Message-ID: <BLU0-SMTP13B70518C27EFD26E898AABC320 at phx.gbl>
> Content-Type: text/plain;	charset="us-ascii"
> Douglas;
> If the light doesn't go off and the reservoir is full, it means that  
> the
> brake assist system isn't coming up to pressure. This could be:
> 1. bad pump
> 2. leaking brake servo
> 3. leaking "bomb" bypass valve
> It could also be a flaky reservoir level sensor or emergency brake  
> sensor,
> but that doesn't sound likely from your description of the symptoms.
> Fred Munro
> '97 S6
> -----Original Message-----
> From: s-car-list-bounces at audifans.com
> [mailto:s-car-list-bounces at audifans.com] On Behalf Of Douglas Fifield
> Sent: June 27, 2009 1:40 PM
> To: Scarlist
> Subject: [s-cars] A Different Brake Light Question
> Gents,
> I also am having brake light problems.  Patient is a 95.5 S6 Avant
> with about 140K miles on the clock.
> Symptom is a brake light that stays on too long when cold starting and
> sometimes does not go off at all when engine is fully warmed in hot
> weather.
> Pentosin reservoir is full (even a little over) when engine is
> running.  Braking feels normal - no pulsing of the pedal.  With engine
> off, I got about thirty pumps of the pedal before it went hard.
> I replaced the brake servo two years ago with a new unit.
> I was leaning toward a bad bomb before doing the pump-down test.
> What's left?  The pump?
> Looking for wisdom in Minnesota.
> -- 
> Douglas in MN
> 95.5 Audi S//6 Avant
> 73 BMW R60/5 mit Toaster Tank

More information about the S-CAR-List mailing list