Re: S6 Brake Light

[quk@isham-research.demon.co.uk (Phil Payne)]

In message <3639a4db.510786@pop3.cris.com> larrye@cris.com (Lawrence Eisenberg) writes:
>I waited a few weeks in disgust and called Audi's help
> number again and after a week's "research" time they called me back
> and this time said it was normal for the light to stay on for 25
> seconds after an overnight or even a3 hour bleed down time.

Bollocks.

The system is leaking down unacceptably quickly.  I wouldn't be too
upset at returning to my car at the airport after a week away and
finding it took a few seconds to clear the light - but half a minute
after three hours?  IMO any visible defect in a braking system is a
safety issue - I'm amazed at AoA's attitude.

My car is over ten years old, the brake system has been brought up to
new specification, and the light doesn't come on even when I leave it
for a week.  I have to discharge the system deliberately to generate the
light.

It probably _isn't_ the accumulator itself, although it might be one
of the valves within it.  It's more likely to be a bad brake servo
unit.  The diagnostic procedure is not well documented for any Audi,
and extending it to cover cases like this is not intuitive.

Basically - park on a flat surface and chock the wheels.  Parking brake
off.  Run the engine until the light goes out.  Turn the engine off and
the ignition back on.  Press the brake pedal repeatedly until the light
comes on.  Should be more than 10 depressions - the light comes on
_before_ the system is discharged, as it is intended to warn you of the
approach of the condition, not tell you when it's too late.

If you get less than ten depressions before the light comes on, or less
than around twenty before the feel of the pedal changes, suspect the
accumulator.

Otherwise, disconnect the return line from the servo to the reservoir
at the reservoir end and watch for drips.  Continuous dripping, even
if it's only a few drips a minute, means a dead servo.  Run the engine
to get some pressure back, natch.

If the servo doesn't leak, turn the engine off and attach a buzzer
(multimeter continuity test will do) to the terminals of the switch on
the servo and take a nap.  When it wakes you, you know the leakdown
time.  Write it on the invoice you send to AoA.

--
 Phil Payne
 Phone: 0385 302803   Fax: 01536 723021
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