Hydraulic Control Assembly - Antilock Brakes: Service and Repair
Removing and Installing Hydraulic Unit
Replacing the Hydraulic Unit
When replacing the hydraulic unit -D-, observe the following points.
- 3 hydraulic unit variants have been installed in the 911 Turbo (996) since the production launch. First version 996.355.955.51, modified version 996.355.955.57 and new/current version 996.355.955.58.
- The first version 996.355.955.51 is no longer available since existing supplies have been used up. Instead of the first version 996.355.955.51 the new/current version with part number 996.355.955.58 should be installed.
- At the first installation of the new/current hydraulic unit 996.355.955.58 instead of the first version 996.355.955.51, ensure that the combination hydraulic unit/rate-of-turn sensor is correct. This means: the hydraulic unit 996.355.955.58 can only be combined with the new/current rate-of-turn sensor (part number 996.606.145.00). Replace the rate-of-turn sensor if necessary.
- For the conversion of the first-version rate-of-turn sensor (part number 996.606.147.00) to the new/current version (part number 996.606.145.00), See Conversion of Rate-of-Turn Sensor.
First version: Rate-of-turn sensor with part No. 996.606.147.00
New/current version: Rate-of-turn sensor with part No. 996.606.145.00.
Removal
NOTE: For the removal and installation of the hydraulic unit -D-, the booster pump -A- of the brake master cylinder -B- and the brake booster -C- remains fitted (installed).
1. Switch off ignition. Remove cover -A- from the hydraulic unit/brake unit.
2. Hold down brake pedal with pedal holder, so that the brake fluid does not run out of the expansion tank completely.
3. To remove the hydraulic unit -D-, carry out the following removal procedure:
- Undo the brake lines on the hydraulic unit.
- Remove the lines between the brake master cylinder intermediate piston circuit and the hydraulic unit.
- Close the brake lines and the brake line connections with suitable plugs.
- Pull off pressure sensor plug.
- Unlock/disconnect the control module plug on the hydraulic unit. Cover the plug connector and the plug.
NOTE:
- In the case of assembly work on the hydraulic connections, the electrical plug connections on the hydraulic unit must always be connected.
- 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.
- Brake fluid on electrical contacts (even thinned brake fluid) leads to corrosion and may cause faults in the system.
- Undo and guide out the hydraulic unit. In the case of unfavourable tolerances, remove the hydraulic unit without the bracket for the hydraulic unit.
Installation
1. Install in reverse order.
NOTE:
- First connect the electrical plug connections on the hydraulic unit, so that the plug connections inside or on the hydraulic unit can not be splashed with brake fluid or water.
- After bleeding, check the assignment of the brake lines/solenoid valves to the correct brake calipers. To do so, call up the PSM system with the PST 2 and carry out a swap test.
2. Bleed the brakes.
NOTE:
- First bleed brakes as usual.
- Do not carry out booster pump activation with the Porsche System Tester 2 until after this has been done (after conventional bleeding) as otherwise damage to the booster pump can occur.
- To bleed at front on right with running booster pump, the bleeding device should remain connected (switched on). Bleeding pressure approximately 2.0 bar.
3. When replacing the hydraulic unit, code the control module (manual transmission/tiptronic).
4. Carry out the following tests:
- Check the system (brake lines and connections) for leaks.
- Read out and erase the fault memory of the PSM control module with the Porsche System Tester 2 (PST 2). Additionally perform the static test in the PSM system.
- Check electrical and hydraulic lines (brake lines) for incorrect assignment using the PST 2.
- Then start the engine. The PSM-related lights in the instrument cluster must go out when the engine is running.
- Carry out a function check of the brakes. Then perform a short test drive and perform at least one ABS control operation, taking the road conditions into consideration. Read out the PSM fault memory again. There must not be any stored faults.