Brake light flashing 5kcs

Fred Munro munrof at
Fri Nov 23 21:39:45 EST 2001

Hi John;

    I had two indications the bomb was dead on my '91 200q. The light stayed
on for over 30 seconds after I started the car (bomb discharged and
repressurizing), and the light flashed under heavy braking (system pressure
too low). The bomb had 3 pumps in it. Replacing the bomb eliminated the
light issues. The car braked normally, but fortunately I had no occasion to
stop in a hurry.
     If the bomb is more than 7 years old, I'd tend to suspect the bomb
before failure of the other components. Without the backup provided by the
bomb, it is possible to pull the system pressure down below the warning trip
for the light with the engine running if you brake hard enough.

Fred Munro
'94 S4

----- Original Message -----
From: "John Larson" <j.d.larson at>
To: <mannix at>; <quattro at>
Sent: Friday, November 23, 2001 8:24 PM
Subject: Re: Brake light flashing 5kcs

> While it's common for listers to suspect the accumulator ("bomb") when the
> pressure warning light flashes, it's the last thing one should suspect if
> happens while the engine is running.  The bomb is merely a reservoir for
> pressure.  If there's insufficient pressure built up by the pump, there
> be insufficient pressure in the system, and correspondingly insufficient
> pressure for the bomb to accumulate.
> My first suspect would be the switch on the booster.  They're cheap
> and I change one every few months.  They often leak, and occasionally
> malfunction.  Most people don't have a way to tap in here to check the
> pressure.
> Wiring would be next.  Plug the wires together and the light should come
> I think, and keeping them apart should make the light stay out.
> Next suspect would be the pump itself.  A gauge is pretty important for
> diagnosing this, mostly because it's pretty expensive.  Mine's marginal,
> it's been that way for 4 years so I guess I can live with the light being
> slow to go out.
> In my car, a 20v, the level and pressure warning circuits are separate, as
> recall (my kid has had it for 6 months, and I'm not sure).  Level warnings
> can be checked by testing the switch and wiring as above.
> The last thing to check would be the bomb.  If the pressure is good, and
> pedal takes 20+ pumps to get firm (engine off), then the bomb is OK.
> no pressure in, no pressure accumulated.  It can't hold pressure it
> have.
> HTH, John

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