Important information

If admission pressure is too high (before a valve is replaced), again build up a slight pressure and, unlike previous test, cause pressure to fall by switching off ignition. Loss of admission pressure should not exceed 0.5 bar within 5 minutes.

After removing manometer, select System Tester menue for drive links / bleeding and let off brake fluid from bleed valves of longitudinal and transverse lock servo cylinders until no more air bubbles appear.

Disconnect System Tester and correct brake fluid level with pressure reservoir completely full (after pump unit has automatically switched off). On no account top up above "max. " mark.

911 Carrera 4 All-wheel drive / Antiblock system

Preventing confusion of longitudinal and transverse lock lines General

- This test ensures that no electrical or hydraulic lines for lock activation/operation have been mixed up. Such a mix-up could for instance occur following an accident repair for which relevant parts (major components, lines and hoses) have been removed.

- System Tester 9288 is required for testing.

- Testing is carried out with vehicle completely jacked up.

Testing

1. Completely jack up vehicle (all 4 wheels free).

2. First check general functioning of transverse lock (correct configuration).

3. Connect System Tester 9288 to diagnosis socket (P. D39/45-9). Switch on System Tester and ignition. Call up PDAS menue for drive links and select "check transverse lock".

Display shows: Transverse lock 1 = Pressure reduction No. of impulses - 0 -.

4. With 0 impulses (display reading) it must be possible to turn rear left-hand wheel. The rear right-hand wheel must be held immobile during testing. Input 1st impulse and turn rear left-hand wheel. Input 2nd impulse and turn wheel etc. With increasing number of impulses, wheel should become harder and finally impossible to turn. With any other result (e.g. wheel does not become harder to turn, even though solenoid valve is audibly being activated with each impulse), start with troubleshooting

5. Check general functioning of longitudinal lock (correct configuration). To do so, engage parking brake and hold front right-hand wheel immobile during testing.

6. With the System Tester select "check longitudinal lock" In menue for drive links. With 0 impulses it must be possible to turn front left-hand wheel (front right-hand wheel immobilised). Input 1st impulse and turn wheel, input 2nd impulse and turn wheel etc. Prescribed reaction: With increasing number of impulses, wheel should become harder and finally impossible to turn.

Procedure for irregularities

- First check whether activation system for lock solenoid valve has been mixed up. To do so, disconnect control unit plug of PDAS/ABS control unit and plug in lock valve block (arrow) with ignition switched off.

D39/45-44

— Carry out continuity test (Multimeter) Prescribed continuity between:

PIN 21 on control unit plug and PIN 3 on solenoid valve plug = line for transverse lock activation

PIN 18 on control unit plug and PIN 4 on solenoid valve plug = line for longitudinal lock activation

PIN Nos. 1...4 for the solenoid valves are marked on the solenoid valve plug and the valve block.

- If this check is in order, the hydraulic lines from the valve block (solenoid valves for longitudinal and transverse locks) to the lock servo cylinders have been mixed up.

- After rectifying this error, carry out another check with the System Tester for additional confirmation.

911 Carrera 4

Brakes - Mechanical

Do It Yourself Car Diagnosis

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