Brake Light?

Fred Munro munrof at
Sat Mar 24 07:05:39 EST 2001

If the brake light comes on at start-up and goes off after a few seconds, it
means your bomb has lost pressure while the engine was stopped.
The bomb can lose pressure via a leaking internal check valve or a leaking
brake servo. The bomb can also have lost it's nitrogen charge, and not be
storing much pressure (typical "dead" bomb).
If you can't detect when power assist goes away with the brake pump test, it
may be because it only takes one pump. The demarcation between assist and no
assist is quite clear - the pedal feel becomes high and hard.
Try the brake pump test with the engine off and the ignition on. See how
many pumps it takes to get the brake light to come on - this will indicate
low pressure in the boost circuit.

If the bomb on your car is original, it is probably dead - they only last 10
years or so.


Fred Munro
'94 S4  128k km

----- Original Message -----
From: "Robert Deis" <rdeis at>
To: <quattro at>
Sent: Friday, March 23, 2001 11:06 PM
Subject: Brake Light?

> 1986 5ktqw, the multi-complaint system is giving me a "brake" warning
> intermittently.  Pentosin and brake fluid levels are both good, and I've
> detected no problems with brake operation.
> Pumping the brake pedal after shutting the car off, I find it very
> difficult to detect that the power assist has gone away, so I'm not sure
> how many pumps it takes..  Operation when I'm driving is fine.
> Most often, the brake warning comes on shortly after startup and goes away
> after a few seconds, but it seems to randomly appear at other times as
> well.
> What's the deal, masters?
> --
> --------------------------------------------------------------------------
>   Rob Deis                  "Let the people know beforehand what the law
>   MiB3347                      is and what they are to expect."
>   rdeis at                              -- 18th Congress, Rec. 75

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