Anti-Lock/Traction Control: Description

CAUTION: See ANTI-LOCK BRAKE SAFETY PRECAUTIONS article in GENERAL INFORMATION.

NOTE: For additional information, see DISC - 7-SERIES article in BRAKES.

Anti-Lock Brake System (ABS) consists of a hydraulic unit with 4 solenoid switching valves, 4 speed sensors, an Electronic Control Unit (ECU), relays and wiring harness. See Fig 1 .

An ANTI-LOCK indicator light, located on instrument panel, lights up when ignition is turned on. Indicator light goes out once engine is started, indicating ABS is ready for operation.

The ASC warning light on the instrument panel indicates the ASC's operating mode:

Light off, ASC ready to operate.
Light flashing, ASC in action.
Light permanently on, ASC passive or defective.

ABS activates at speeds greater than 8 MPH. When vehicle speed is greater than 3 MPH, the built-in electronic test monitor will start checking ABS. If fault is found, warning light will come on. When ABS light is on, ABS is switched off. Vehicle will then convert to conventional braking.

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

With the introduction of the M60 engine, a change in ASC+T operating parameters becomes necessary. The previous interconnected driving management system of Engine Control (DME), Throttle Control (EML), Slip Control (ABS/ASC+T), and Transmission Control (EGS) is not possible with the 740i/iL due to the absence of an EML system.

The 740i/iL is therefore equipped with an Auxiliary Throttle Valve Control system (ADS II) to allow ASC/MSR regulation in the event of excessive wheel slip during acceleration or engine braking.

The ASC+T system as installed on M60 equipped vehicles makes use of three components which comprise the Auxiliary Throttle Valve Control system (ADS II):

A choke-valve plate assembly (auxiliary throttle valve) which is normally held open by spring pressure, mounted upstream of the throttle body. See Fig 2 .
An ADS II actuator which closes the choke-valve plate by action of a bowden cable. See Fig 3 .
An ADS II Control Module which controls the ADS II Actuator.

The ADS II actuator is mounted forward of the left front wheel well, and the ADS II control module is mounted in the right-hand kick panel.

Fig 1: Identifying Anti-Lock Brake System Components

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Auxiliary Throttle Valve

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 3: ADS II Actuator

Courtesy of BMW OF NORTH AMERICA, INC.