Note

Rubber mounts on speed sensors are connected with wire covers in precise position. Take speed sensors out of protective packaging only briefly before installation (loss of permanent magnetism). Make sure that there are no foreign metal particles (burrs) on magnetic edge of speed sensor before installing. 2, Place speed sensor in wheel carrier without application of force and mount with socket head screw. 3. Clip wire in holders on wheel carrier and rear axle cross member. 4. Connect wire plug...

Central Valves Operation

In off position both central valves are open through position on adapter sleeves (1). Brake fluid can therefore flow into system. If brakes are applied, i. e. brake master cylinder pistons moved to the left, both central valves are closed and brake pressure can be built up. If driver Lakes his foot off of brake pedal, pistons return to their original position and central valves will be opened after contact with the adapter sleeves. O 20 4 0 60 SO 100 120 140 160 1B0 O 20 4 0 60 SO 100 120 140...

Pressure Dropping Phase

If the braked wheel still tends to lock in spite of constant hydraulic pressure, e. g. because of road surface changing from dry to slippery, pressure in wheel brake cylinder must be reduced. Current higher than approx. 5 amperes on the electric solenoid valve causes a greater piston stroke, which opens the outlet. Hydraulic fluid flows to pump reservoir and return delivery pump. Return delivery pump returns the brake fluid into the brake master cylinder against existing pressure. A damper is...

Braking Test Stand

2 control umt plug auxiliary leads, approx, 60 cm long, with 2 insulated clips and 2 flat male plugs, N 17.457.2. Always use auxiliary lead for tests on control unit plug. Control unit multiple pin plug with view ot plug terminals. 17 16 15 V 13 12 II IQ S 3 _7_ 6 5 1 V 1 J' 17 16 15 V 13 12 II IQ S 3 _7_ 6 5 1 V 1 J'

Installing

Place brackets for hydraulic unit in wheel housings and till down on wheel side. 2. Move hydraulic unit into brackets from wheel side and insert two mounting bolts (position of mount as described in point 1). 4. Finish installation of hydraulic unit on bracket. Tighten three mounting bolts. 5. Mount brake pressure regulator and brake lines on hydraulic unit in correct position. If applicable, hold brake lines in brackets on wheel housings with clips and engage locks.

Removing

Remove intake hose on air cleaner. 2. Turn off ignition, take wire plug out of holder in engine compartment and disconnect. 3. Remove front exhaust shield (to make procedures easier), Unclip wires on wheel housings and pull out with rubber grommet in direction of wheel. Also pull out rubber grommet for brake line. 4 Unclip wire on side member and in holders on steei ing knuckle. Unscrew socket head screw and pull speed sensor out of steering knuckle.

Safety Circuit

The safety circuit will detect erroneous signals in the electronic control unit as well as defects in wire harness and plug connections on hydraulic unit and relays, ABS is switched off when a shortcoming occurs. A shortcoming is shown when indicator lamps come on. The safety circuit also monitors battery voltage constantly. If battery voltage drops below the specified value, ABS will also be switched off until battery voltage again reaches the specified value. In addition to the monitoring...

Tester

1 - Digital LED display unit, 3 1 2 digits 2 - Lamp 1 (green) battery voltage okay Lamp 2 (red) battery voltage too low 3 Lamp 3 (green) motor arid valve relays as well as overvoltage protection okay Lamp 4 (red) motor and valve relays as well as overvoltaye protection 5 - Push button set for channel (wheel) selection 5-1 Front axle

Important

Always perform all test steps beginning with test step 1. Test steps 23 and 24 must be performed prior to test steps 20, 21 and 22. A braking test stand is required for test steps 20 through 23 *). Also conform with following points. 1. Never operate car as long as tester is connected. 2. Test stand rollers and car tires must be dry during test. 3. Selector lever of a car with automatic transmission must not be in park position while testing rear axle. 4. Never use a brake pedal winch to adjust...

Front Speed Sensor

Wire of front speed sensors is routed via bracket (2) on steering knuckle . to bracket (4) on side member and from there it continues through wheel house wall into engine compartment to a wire plug. Plug is mounted on shock absorber bracket with clips. 6 Plug (brake pad wear indicator) Wire ol rear speed sensors is routed from a double holder (7) on wheel carrier . to a bracket (81 on rear axle cross member and continues from here in an arc to wire plug (9). Holder for wire plug is mounted on...

Removing Note

In left-hand drive vehicles the electronic control unit is located on the driver's side, above the hood release on the side panel of the footwell In right hand drive vehicles the electronic control unit is located above the central fuse relay board. 1. Move back seat and pull up steering wheel (to make job easier). 2. Press spring-loaded lock and pul plug off of electronic control unit. 3. Take electronic control unit off of bracket after unscrewing mounting nuts. 1. Mount electronic control...

Test Cycle

Porsche 928 Ceb

An integrated test program runs off in the control unit when switching on ignition. A further test program runs off at a road speed of 6 krn h. Testing at 6 km h can be felt, since pump in hydraulic unit will run briefly. Test cycle is repeated each time car moves off, if ignition had been turned off previously. Testing includes electronic control unit, hydraulic unit, speed sensors, relays and wire harness. A shortcoming is shown by the ABS indicator lamp coming on. If the shortcoming is...

Connecting Tester

Turn off ignition and pull off multiple pin plug (35-pin) (2) on electronic control unit (1 > Control unit remains installed. 2. Connect multiple pin plug (2) of electronic control unit with plug (3) of tester. 3 Connect plug (4) ol tester on electronic control unit (1) so that spring-loaded lock is heard to engage on plug, 4. Turn on ignition all other electric equipment must be switched off.

Relay Operation

A ABS-relay C has overvoltage protection in form of a Zener diode. When reaching an overvoltage of 22 V e. g. defective alternator , this diode will be conductive and prevents further increasing in voltage. This protects control unit against damage from excessive voltage. b Solenoid relay d closes when ABS control unit receives voltage from alternator. This causes ground connection of relay term. 85 via the control unit. Relay switches over and supplies battery 30 to solenoid valve coils. If...

Pressure Holding Phase

If the braked wheel reaches the lock limit by way of hydraulic pressure from the brake master cylinder, further pressure increase in the wheel brake cylinder will be prevented. The solenoid will receive current of approx. 2 amperes, valve piston is activated and outlet as well as inlet of solenoid valve are closed. Hydraulic pressure between hydraulic unit and wheel brake cylinder remains constant. brake c Electric solenoid valve, front, right d Electric solenoid valve, front, left e Electric...

Test Program

Electronic Brake Force Wire Hardness

General Information 1 ABS in Operation 2 ABS in Porsche 928 3 Main Features 5 Hydraulic Unit 7 Speed Electronic Control Wire Harness, Relays, Overvoltage Stop Light Switch Brake Master Cylinder Brake Pressure Regulator Wiring General Hydraulic Unit Removing and Electronic Control Unit Removing and Installing v . . 33 Speed Sensors Removing and Testers and Tools Tester Test Steps 1-24 PORSCHE 928 S with Antiblock System ABS The antiblock system is an important contribution to improvement of...