On-Board Control System (OBCS) Unit (BMW 5 Series E12)

Some cars were equipped with a BSC unit installed on the roof in the area of the interior rear-view mirror. The BSC unit consists of an electronic control circuit, seven LED indicators, above which their function is indicated, and a TEST key for checking the operability of the indicators. If there is a malfunction in any of the circuits monitored by the BSC, the corresponding LED lights up and at the same time the CHECK CONTROL indicator lights up in a yellow flashing light in the instrument cluster.



On the BSC panel, the alarms are located in the following order:

• 1st row (top down): brake light bulb health indicators (8REMSLICHT), serviceability of the side light bulbs in the rear lights (RCCKUCHT), serviceability of the license plate lights (KENNZEICHENLICHT);
• 2nd row (top down): low beam headlight bulb health indicators (ABBLENDLICHR), windshield washer fluid level (WASCHWASSET), coolant level (KCHLWASSER);
• 3rd row (top down): oil level indicator (MOTOROL), backup indicator, self-test key of the BSK (TEST).

Operating principle of BSK

When the ignition key is in position "1", all indicator labels light up. When the oil, coolant or windshield washer fluid level is low, the corresponding indicator lights up.



When the ignition key is in position "2", all the indicator labels light up, the CHECK CONTROL display in the instrument cluster lights up with a yellow flashing light and the brake light lamp serviceability indicator lights up (BREMSLICHT). Before turning the key to position "2", do not press the brake pedal, otherwise the BSK will not be able to check the serviceability of the brake light bulbs. After pressing the brake pedal, the CHECK CONTROL display and the brake light serviceability indicator go out.

To check the low beam headlights, tail light bulbs or license plate lights before driving, start the engine and turn the appropriate switch or circuit breaker to the on position. If any of these circuits are faulty, (the fuse or lamp has blown), the corresponding indicator lights up.

To check the brake light circuit (to make sure the fuse or bulbs are not blown) press the brake pedal: the CHECK CONTROL display, indicator labels and the brake light indicator go out, but only if the corresponding circuits are in good condition.

If the BSC detects malfunctions in the controlled circuits when the vehicle is moving, the CHECK CONTROL board lights up with a yellow flashing light, all the inscriptions on the BSC panel are displayed, and the corresponding or corresponding indicators light up.

The performance of the indicators is checked by pressing the TEST key, and the indicators should light up. After releasing the key, only the indicators in the circuits they control remain lit, the CHECK CONTROL display goes out. After some time, the inscriptions on the BSK panel go out.

After turning the ignition key to the "O" position, the previously lit indicators of faulty circuits go out. Faults detected by the BSK in the monitored circuits are remembered. When the key is in the "1" position and the external lighting is turned on, the corresponding indicators light up again.