ELECTRONICALLY CONTROLLED HYDRAULIC SYSTEMS
BOSCH ABS
38
HYDRAULIC BRAKING TEST
This section describes the test to be carried out using the XR25, to check the mounting of the ABS system in
the vehicle and, in particular, the hydraulic circuit.
NOTE: for this test, two persons are required and the vehicle must be on a two post lift, if possible.
Principle of the test
Put the vehicle on the lift with the wheel to be tested raised. One of the operators must be in the passenger
compartment in the driver’s position with the XR25. Switch the ignition on, vehicle in neutral, in fault finding
mode and press the brake pedal. The second operator must apply a torque to the wheel to try and rotate it.
The operator generates an appropriate command on the XR25 which carries out the following cycle ten
times: alternate decrease then increase in pressure at the wheel to be checked. These actions in the ABS will
be noted at the wheel as ten alternate locking and releasing operations. The jerky movement of the wheel,
noted qualitatively by the operator, signify that the hydraulic circuit for this wheel is correctly connected.
The programme for the XR25 for this sequence is as follows:
- Cycle on the wheel to be tested:
- a drop in pressure for 200 ms where the pump starts at the same time,
- an increase in pressure for 300 ms where the pump starts at the same time (ten cycles are carried out
for the wheel in question).
- The pressure increases to master cylinder pressure for all four wheels.
- The hydraulic pump motor stops.
- The operator releases the brake pedal.
The hydraulic test for the wheel in question is complete - begin the test for the three other wheels.
BLEEDING PROCEDURE
NOTE :
the hydraulic assembly is pre-filled.
This bleeding procedure must be used when one of the following components has been removed:
- the hydraulic assembly,
- the master cylinder,
- the pipework (between the hydraulic assembly and the master cylinder).
1)Bleed the braking system conventionally using the pedal.
NOTE : if, after a road test with ABS regulation, the pedal travel is not correct, bleed the hydraulic assembly.
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