Checking the locking torque friction coefficients of the longitudinal and transverse locks

In the event of functional problems or irregularities, perform or verify test points 1, 2 and 3 before the locking torque test (locking torque in relation to pressure).

This means:

- No fault stored in the control unit fault memory t

- Perfect bleeding condition of the lock control

- Thickness of the disk assemblies ok (wear assessment)

If the friction coefficient curves deviate from the setpoint in the locking torque test, the lock is not functioning optimally. Only a large deviation of the actual value from the setpoint is stored as a system deviation in the control unit fault memory.

When performing the locking torque test, check the pre-pressure valves in the lock hydraulics (lock actuation system) as well (test point 5).

Test point


Test point 5

Checking the pre-pressure valves in the lock hydraulics (lock actuation system)

A pre-pressure valve is installed in the pressure line before every lock cylinder.

This holds a residual pressure for play compensation and to ensure dynamic driving response.

Test point 6

Pressure test on the booster circuit (brake booster and lock control)

The following are tested:

- Freedom from leaks of the booster circuit

- Pressure accumulator (gas charging pressure)

- Switching points for the booster circuit (brake pressure warning lamp No. 13 and operating pressure)

Brake pressure warning lamp No. 13, refer to Page D39/45-3 under test point 1.

Frequent operation of the pressure pump:

It is normal for the pressure pump (pump assembly) to start running after every 2nd or 3rd braking operation.

Test point 7

Longitudinal and transverse acceleration sensors

This test serves the purpose of verifying the following points:

- Correct installation position of the sensors

- Function of the sensors

- Connecting cables (connectors) plugged onto the correct sensor in each case (confusion check)

The sensors can be damaged by extreme acceleration (throw-fall-shock stressing) or extreme deceleration (accident).

A sensor test must be performed in such a case and after repair work (removal and installation) (P. 45-1)

Test point


Test point 8

Preventing confusion of of longitudinal and transverse lock lines

(hydraulic and electric)

This test tensures that in each case the right lock is operated following activation from the control unit. Electrical lines from the control unit to the valve block (longitudinal and transverse lock solenoid valves), or hydraulic lines (pressure lines) from the valve block to the lock cylinders could be mixed up. This could for instance occur following an accident repair involving corresponding removal and reassembly work.

Test point 9

ABS test

If a fault is indicated by the PDAS/ABS warning lamp, first read out the control unit fault memory with the system tester 9288. To remedy the fault, use the ABS 2-LED tester in conjunction with the 55-pole adapter cable if necessary. The adapter cable is also used for sensor testing. After repair work on ABS components (as known from 944 and 928), perform a test with the ABS 2-LED tester under all circumstances.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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  • christina bolding
    How to replace transversal sensor 964 carrera 4?
    7 years ago
  • petra
    What is function of pdas locks 964 c4?
    5 years ago

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