2. Other checks require a pressure gauge, therefore it is best to contact an Audi dealer for this work. However, if a pressure gauge is available, the procedures are given in the following paragraphs.
3. Relieve all pressure from the feedback hydraulic actuator by depressing the brake pedal with the engine off approximately twenty times.
4. Disconnect the electrical wiring from the differential pressure indicator, then unscrew the switch, remove the washer. Connect the pressure gauge.
5. Run the engine at idle speed until the pressure is approximately 140 bar.
6. Turn off the ignition, then pump the brake pedal, observing the pressure gauge. The pressure should drop slowly at first and then suddenly drop to zero. The pressure before dropping to zero is the pressure of the accumulator, and if it is less than 30 bar, the accumulator must be replaced.
7. If the pressure specified in point 5 is not reached, first check the tension of the pump drive belt, referring to Chapter 2 of Section 10.
8. If the tension of the drive belt is correct, check the performance of the pump by connecting the special hose and the restrictor (VAG 1354/1) to the pressure outlet of the pump. With the engine idling, the pumping rate should be at least 0.3 liters per minute. If not, replace the pump.
9. Remove the special hose and restrictor, install the pump outlet pipe.
10. The accumulator includes unloading and one-way valves. If the pump performance is normal, but the pressure given in point 5 cannot be reached, the unloading valve is defective and the accumulator must be replaced.
11. To test the one-way valve, run the engine at idle speed until maximum pressure is reached. Switch off the ignition, bleed the brake pedal until the pressure is approximately 135 bar. Check that the pressure does not fall below 130 bar within five minutes. If the pressure drops below 130 bar, the valve is defective and the accumulator must be replaced.
12. At the end of the check, remove the pressure gauge, install the differential pressure indicator with a new washer, if necessary. Reconnect the wiring.
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