There are two possible ABS units in the 928.
The 928.618.118.00 which is the old style used in cars prior to 1990,
and the 928.618.120.01 which has PSD combined with ABS. The difference can easily be seen, it has an extra row of pins.
The 928.618.120.01 has diagnostic features and can be operated from a handheld OBD tester or from a computerized tester.
Here's a screenshot from a ABS/PSD.
|55||Free||37||Ground, ABS solenoid valves, front left + rear axle||19||Operation of ABS solenoid valve, front left|
|53||Speed sensor output at front right for RDK control unit||35||Operation of instrument cluster: PSD off||17||Monitoring, voltage supply for ABS solenoid valves|
|52||Electronics ground||34||Signal from lateral acceleration sensor||16||Speed sensor output at front right for
RDK control unit (*)
|51||Free||33||Free||15||Voltage supply (+5v) for acceleration sensor|
|50||Signal, speed sensor at front left||32||Free||14||Free|
|49||Free||31||Pump motor monitoring (hydraulic unit)||13||Free|
|48||Ground, shield, speed sensor at front left||30||L-wire from diagnosis||12||Speed sensor output at rear left for RDK control unit (*)|
|47||Signal, speed sensor at front right||29||Brake light switch||11||Voltage, terminal 30|
|46||Ground, shield, speed sensor at front right||28||Free||10||Speed sensor output at rear right for RDK control unit|
|45||Signal, speed sensor at rear left||27||+D (Terminal 61 / charge)||9||Ground of acceleration sensor|
|44||Ground, shield, speed sensor at rear left||26||Free||8||Free|
|43||Signal, speed sensor at rear right||25||Free||7||Operation of valve relay on hydraulic unit|
|42||Ground, shield, speed sensor at rear right||24||Operation of ABS warning lamp||6||Free|
|41||Free||23||Monitoring of supply voltage for lock solenoid valve||5||Operation of pump motor relay on hydraulic unit|
|40||Indicator lamp green for PSD function||22||Operation of ABS solenoid valve, front right||4||K-wire from diagnosis|
|39||Free||21||Operation of transverse lock solenoid||3||Ground, ABS solenoid valve, front right|
|38||Free||20||Voltage for valve and motor relays on hydraulic unit||2||Operation of Rear-axle valve solenoid|
|1||Voltage, Terminal 15|
|(*) Additionally to vehicle speed. Pin 16 (front left) on mod. 1991/1992 and Pin 12 (rear left) as of mod. 1993|
ABS ecu location on a GTS