Anti-Lock Brake System: Description

The Mercedes-Benz Anti-Lock Brake System (ABS) is a Bosch design. It operates from the interaction of a hydraulic unit with 3 fast-switching solenoid valves, 3 speed sensors, an electronic control unit with overvoltage protection and a wire harness with relays.

A Yellow warning light with the "ABS" symbol, on instrument panel, lights as the ignition is turned on. The ABS warning light will go out once the engine is running. The ABS system is programmed to activate after 7.5 MPH.

When vehicle speed is more than 3 MPH, Built-In Test Equipment (BITE) will begin check of ABS. If any fault is found, the warning light will again go on. When warning light goes on, ABS is switched off and vehicle will brake without ABS control. The conventional brake system remains operational.

If battery is less than 10.5 volts, when ignition is turned on and test speed exceeded, ABS will remain off until alternator increases voltage to more than 10.5 volts. Warning light will then go out.

Following repair, during which no direct components of ABS were involved, a simple light test will check system. Check that light goes out after 7 MPH.

NOTE: The entire ABS system must be checked if repair includes any ABS component or if units are replaced following an accident. Use ABS Test Adapter 126-859-09-21-00 together with brake test bench.