Examination
Switch on the ignition and press the brake pedal.
If the brake lights don't come on, check the fuse first. Then check the bulbs. If the corresponding lamps are not burnt out, check the brake light switch.
To do this, remove the lower left trim (above the pedal).
Disconnect the connector from the brake light switch while squeezing the tabs.
Turn on the ignition.
Jumper both brake light switch wires. If the brake light does not come on, adjust or replace the brake light switch.
Withdrawal
Disconnect the connector from the brake light switch while squeezing the tabs.
Loosen the brake light switch on the pedal support, do not remove the bolt.
Use your fingers to pull out the button and the red locking sleeve of the switch in the direction of the arrow so that the lugs -6- can be pressed together.
Press tabs together and pull brake light switch -7- out of holder -8-. 9 clutch pedal switch, installed only on vehicles equipped with the Tempomat system.
Installation
Insert the switch with the bushing completely out into the pedal support and click into place.
Slide the red locking sleeve into the switch until the lug of the sleeve rests against the pedal support.
Screw the fastening on the pedal support.
Connect and lock the connector.
Check that the brake lights come on with the ignition on and pressing the brake pedal.
Install the bottom cover.
ABS system
Depending on the model and composition of the equipment, the MARK IV anti-lock brake system manufactured by TEVES can be installed on BMW cars. Since September 1991, the ABS system has been installed on all mass-produced cars. It is not possible to retrofit the vehicle with ABS.
The ABS system prevents the wheels from locking during heavy braking. Thanks to this, with full braking, the controllability of the car is fully maintained.
The ABS system is ready for operation when the ignition is switched on and speeds from about 8 km/h. It controls all braking processes in the blocking area
Placed on each wheel, two speed sensors measure the speed of rotation of the wheels. Based on the signals from the individual wheels, the control unit calculates an average speed that roughly corresponds to the speed of the vehicle. As a result of comparing the rotation speed of an individual wheel with the average rotation speed of all wheels, the ECU determines a wheel slip state, and thereby can determine that the wheel is approaching a lock state.
As soon as blocking begins, i.e. when the pressure in the brake caliper is still too high in relation to the adhesion of the wheel to the road surface, the control unit maintains a constant fluid pressure based on signals from the speed sensors. This means that the pressure in the brake caliper does not increase even with a stronger pressure on the brake pedal. If the blocking tendency persists, the brake fluid pressure is reduced by opening the outlet valve. At the same time, it opens just enough so that the wheel begins to rotate again, then the pressure is again maintained constant.
If the wheel speed exceeds a certain value, the hydraulic system again increases the pressure, but without exceeding the braking pressure, which is created by the driver when the brake pedal is pressed.
This process is repeated for each wheel until the brake pedal is released or until the vehicle almost stops (about 3 km/h).
The control circuit in the electronic control unit ensures that the ABS system is turned off when it fails (e.g. broken wire) or when the supply voltage drops (battery voltage below 10.5 volts), which is indicated by the ABS warning light on the dashboard. In this case, the braking behavior of the vehicle is the same as if the ABS system had not been installed.
When the ABS warning lamp comes on (ABS shutdown alarms) pay attention to the following points:
- Stop the car, turn off the engine and start it again.
- Check battery voltage. If the voltage is less than 10.5V, charge the battery.
Caution: If the ABS warning light comes on at the beginning of a trip and then goes out, this means that the battery voltage was initially low and then increased due to the charge from the alternator.
Raise the car, remove the wheels, check the integrity of the electrical wires of the speed sensors (no fraying).
Have the ABS system further checked at a workshop.
Attention: Before carrying out electric welding work, disconnect the connector of the electronic control unit. Disconnect the connector only when the ignition is switched off. During painting work, the control unit may only be exposed to temperatures up to a maximum of 95°C for a short time and for a long time (up to about 2 hours) exposed to temperatures up to a maximum of 85°C.