Description of On-Board Diagnostics

Microprocessor-Controlled Antilock Brake System (uC-ABS):

Notes:

These troubleshooting instructions only refer to the microprocessor-controlled antilock brake system

Notes on the BMW DIAGNOSTIC SYSTEM:

General

The ABS warning lamp lights constantly during the diagnostic procedure. Use the 35-pin universal adapter for troubleshooting.

Defect Code Memory

Certain defects are not stored before a certain speed threshold has been exceeded although they may already exist when the vehicle is stationary.

If three speed sensor defect codes are stored simultaneously with the same ambient/storage conditions, this may be an indication that a "finish balancer" was used to balance the wheels. In this case, there is no real defect in the ABS system, i.e. the defect code memory can be cleared.

Other Diagnostic Program Functions

When a defect exists, only the function "read/clear defect code memory" can be activated; diagnostic mode is not fully operable before switching the ignition off and on again, provided the defect detection criteria still do not or no longer exist.

On vehicles equipped with a differential lock, application of the test procedures "speed sensor interchange test" and "function test hydraulic unit" are of little use on the rear axle since the rear wheels cannot be turned separately.

Troubleshooting:



Troubleshooting for the above specified defects is performed with the diagnostic program in the BMW DIAGNOSTIC SYSTEM in accordance with the screen display.

Notes:

If the ABS lamp flickers while driving but no defect code is stored in the defect code memory, then this indicates temporary under voltage in the ABS system.