hydraulic brake booster
If the pressure warning light comes on, this can be caused by a leaking brake booster. Depressurisation and limited braking assistance may become the result.
Hydraulic brake boosters are usually long-lasting components and are rarely the cause of malfunctions. More often, the problem lies with the brake pressure accumulator. The brake booster can be checked in situ. If no external oil loss towards the brake master cylinder or brake pedal is recognisable, the return flow of the brake booster must be checked. To do this, switch off the engine after idling for about two minutes. Do not depress the brake pedal. Now disconnect the return line to the oil reservoir directly at the brake booster. No large quantities of oil may now escape from the return port. Only droplets are permitted. If hydraulic oil trickles or splashes out of the return line, the brake booster is defective and must be replaced or repaired. Repair is possible in many cases.
Tip: If the brake booster is defective, the condition of the pressure accumulator cannot be checked in situ.