Hydraulic Reservoir Fluid Low? Brake Accumulator (Bomb) Defective?
The BRAKE warning light will normally come on when the ignition is first turned on, and then will go out after the engine has been started and the emergency brake lever is completely released.
This light can come on if your brake master cylinder reservoir is low on brake fluid, if the hydraulic reservoir is low on Pentosin Mineral oil, or if your hydraulic brake booster system is low on pressure. If your instrument panel Brake warning light flashes briefly when you first hit the brake pedal while driving, you may have a defective Brake Hydraulic Pressure Accumulator.
This Accumulator is also called the Brake "Bomb" as it is shaped like a small hand grenade. It is a round canister with a nitrogen charged area sealed by a diaphragm. This brake accumulator is designed to store hydraulic pressure for Power Brake assist when the engine is running, but most importantly when the engine is not running. It is mounted underneath the drivers side frame rail, below the engine compartment.
It is useful and required in cases when emergency stopping is required, should the engine die while driving. It also gives some hydraulic assist during the initial application of the brakes while stopping the car with the engine running.
One test for the accumulator, is to run the engine for a few minutes, turn off the engine, and then pump the brake pedal until the pedal feels hard, (no more power assist). Normally with a good, working brake accumulator, this test takes 25-35 pumps on the pedal before the pedal gets hard. If the pedal gets hard with only a few pumps on the pedal, the brake accumulator is defective and should be replaced.
Note: There was a change in 1989 on the Audi 100/200 to a new style brake accumulator which uses O-ring seals at the hydraulic lines, instead of the metal crush washers used in the 1986-88 5000/T/Q vehicles.
