Hydraulic Control Assembly - Antilock Brakes: Service and Repair
Removing and installing hydraulic unit
The -hydraulic unit- is installed in the radiator tank on the front right, under the DME control unit.
General information
Caution! After installation of the brake master cylinder or the hydraulic unit, the pressure sensor must be calibrated with the Porsche System Tester! The PSM does will not work without values for the current brake pressure.
After fitting the hydraulic unit, a static test (swap test), must be carried out with the Porsche System Tester.
Note!
^ When fitting the hydraulic connections, the electrical plug connections on the control units must remain connected as long as possible. This prevents the plug connections on the hydraulic unit or in the plugs inside from being splashed with brake fluid or water.
^ Any damp plug must be wiped dry before being disconnected from the plug on the hydraulic unit. If necessary, provide the plug with a suitable protector.
^ Brake fluid on electrical contacts (even thinned brake fluid) leads to corrosion and may cause faults in the system.
^ The brake lines must not be bent in the area of the hydraulic unit.
^ Clean the interfacing points of the brake lines, but not with cleaning agents.
^ Rinse any brake fluid emerging thoroughly with water.
Removal
1. Remove radiator tank covers. Using the bonnet stay 9704 the bonnet can be opened wider for better accessibility of the radiator tank. To do this, remove the front pneumatic spring and mount the bonnet stay (2 workers required).
2. Remove -DME control unit.
3. Release the -ground cable (arrow)-, unclip the wiring harness and set it aside.
4. Remove the -holder for the DME control unit (arrow)-.
5. Remove the housing of the intake air duct. To do so, unscrew both external fastening nuts and both retaining clips in the inside of the air duct.
6. Provide a suitable protector for the control unit connector.
7. Activate the brake pedal by hand using the brake pedal loader, (do not clamp it yet!). Plug the vent hose of the vent bottle onto the front left and rear left bleeder screw of the brake calliper (2 workers required). Open the bleeder screws until the brake pedal is completely pressed down. Tighten the brake pedal loader and close the bleeder screws. This will close the central valves of the tandem brake master cylinder so that only a little brake fluid can flow out of the opened brake system.
8. A sufficient number of cloths should be put under the hydraulic unit to absorb any brake fluid emerging. If some runs into the radiator tank nonetheless, immediately rinse thoroughly with water.
9. Mark the -lines on the hydraulic unit- (colour marking, etc.) and remove. Seal the loosened lines with suitable plugs.
10. Pull off the control unit plug from the control unit.
11. Remove the hydraulic unit (SW 8) and take out of the holder, upwards.
Installation
Note!
^ Install in reverse order.
^ Remove the plugs on the new hydraulic unit after the respective brake line is fitted.
^ Use correct tightening torques.
1. Bleed the brake system. To ensure the full function of the brake system, drain approximately 250 ccm brake fluid from each wheels.
2. Calibrate the pressure sensor with the -Porsche System Tester-. To do this, select in the menu >> PSM >> Calibration >> Pressure sensor<<. The safety code is displayed in the Porsche system tester under Menu >> PSM >> Actual values <<.
3. Perform a swap test with the Porsche System Tester. To do this, select in the menu >> PSM >> Function selection >> Drive links <<.
4. When replacing the PSM control unit, it must be coded with the Porsche System Teste. The safety code is displayed in the Porsche system tester under Menu >> PSM >> Actual values <<.
5. Perform a function test. During the test drive, perform at least one ABS control operation, taking the road conditions into consideration. Read out fault memory There must not be any stored faults.