B: Driving with ABS
The malfunction indicator lamp with the ABS symbol in the instrument cluster lights up when the ignition is switched on and goes out after the engine is started (same as charge-indicator lamp).
Should the lamp fail to go out, this could indicate low voltage in the vehicle electrical system or an open circuit in the current supply to the electronic control unit. Once the vehicle has attained a speed of approx. 5 km/h, the ABS performs a self-test (BITE = B uilt I n T est E quipment). The ABS malfunction indicator lamp will light up if a fault is recognized.
If the problem assumes the form of a permanent fault, e.g., open wire, then the fault remains stored in the ABS control unit until the ignition is switched off. Short periods of undervoltage in the vehicle's electrical system are not recorded. Thus, if the battery voltage remains below 11 volts after the ignition has been switched on and the vehicle has exceeded the test speed, the ABS will remain inactive until such time as the alternator raises the system voltage to above 11 volts. Only then will the ABS malfunction indicator lamp go out.
Any braking in the locking range initiated above 8 km/h (above 12 km/h on the 1st version up to 02/84) can be governed down to a speed of 3 km/h (down to 5 km/h on the 1st version up to 02/84). This means that controlled braking will proceed only after the so-called control speed of 8 km/h (12 km/h on 1st version up to 02/84) has been exceeded.
When the malfunction indicator lamp in the instrument cluster is on, this signals that the ABS is inactive; the antilock system will not operate when the vehicle's brakes are applied. The conventional brake system remains operational. The vehicle should be checked and repaired in a Mercedes-Benz service station as soon as possible.
Design
The anti-lock braking system comprises the conventional braking system known up to now and the following additional components:
- Hydraulic unit
- Wheel speed sensors
- ABS control unit
- Harness with overvoltage protection relay