Function Check

Function Check:

After switching on the ignition, the ABS indicator lamp lights. After the engine has started, the indicator lamp must go out when the antilock brake system (ABS) is OK.

This procedure is repeated every time the ignition is switched off and on. If an electrical or electronic defect is found, the control unit automatically switches over to "normal brake". This means the car can still be braked but without the antilock control (wheel locking possible!). This situation is indicated by the ABS indicator lamp lighting constantly in the instrument cluster.

It is necessary to check the function when the ABS warning lamp does not go out, if it lights during driving or it does not light when the ignition is switched on or when working on the ABS system.

The function check is carried out with the BMW Service Tester. By way of a corresponding connector, the test unit is connected to the wire harness and to the control unit. Refer to microfilm - ABS Nominal Values.

Important!

The device connector must be detached and attached only when the ignition is switched off. Refer to Wiring Diagram.

Care must be taken before carrying out the function test to ensure the conventional brake system (hydraulics, brake pads, lines etc.) is in working order. In addition, the power supply must be ensured (battery voltage, alternator function, relay function). The relay drive is fuse protected.

The Antilock Brake System (ABS) control unit continueously monitors the system electronics and wiring harness for possible defects. The system must be checked if:

- The ABS indicator lamp does not illuminate when the ignition is turned "On"
- Extinguish after the brief test
- Illuminates while driving

When a fault is detected, the ABS indicator lamp will illuminate to notify the driver of a system malfunction and the ABS control unit will shut down the anti-lock function, "fail safe", assuring normal use of the conventional brake system. The ABS system will not resume standby mode until the related malfunction is corrected.

NOTE:
If the ABS warning lamp remains "On", then a fault is indicated. When the fault has been repaired, the lamp will go "Out". There is NO procedure for turning the lamp "Off".

When testing the anti-lock brake system, ensure all other electrical components are turned "Off", and that the ignition switch is in the "Off" position before connecting diagnostic equipment.