Active Cruise Control

Active Cruise Control


Notes on function
For the active cruise control (ACC), the gap to the vehicle ahead is measured by a radar sensor (ACC sensor). The detection range lies between approx. 2 - 120 metres.
The active cruise control can be activated as of 30 kph.

Longitudinal dynamics management control unit (LDM)
The LDM control unit has the following tasks in the ACC function:
- Cruise control if the ACC sensor has not picked up a vehicle ahead.
- Implementation of ACC requests for acceleration and braking.
- Fault monitoring of the ACC system by means of plausibility check of the signals.

Fault situations
A precondition for the function of the ACC is that the engine / electronic transmission control and the DSC are operating without faults. For this reason, there is a continuous check as to whether the acceleration or braking requests are carried out without faults. In the event of a fault, the ACC is switched off.
Heavy soiling of the ACC sensor can mean that the function cannot be activated or the ACC is deactivated. The ACC sensor must be adjusted horizontally and vertically in the installation location so that objects can be picked up without faults. This ACC sensor setting must be made on a special setting bay using special tools approved by BMW.
The service function "Set ACC sensor" is available for the setting.
A poorly adjusted ACC sensor is detected. A fault is stored in the ACC fault memory. The ACC cannot be activated until the sensor is correctly set.

Special situations
If the ACC is active and the vehicle remains below the set speed or does not accelerate, this can have the following causes:
- Maximum lateral acceleration in curve of 3m/s2 reached.
- Strong visual impairment due to rain, fog or snow. This can also lead to deactivating of the ACC function.
- High crown or dip in the course of the road.
- Reflection of the radar waves on tunnel walls or crash barriers.

Lens heating
The lens is heated to ensure the ACC is effective in winter and in poor weather conditions. This system is designed as a resistance heating system with the heating coil integrated in the plastic body of the lens. After the engine start, the lens heating in all ACC shift modes is switched on depending on the ambient temperature. To prevent the lens body from overheating, the lens heating system is switched off when the temperature inside the unit exceeds 50 °C. The temperature is measured by the interior temperature sensor of the ACC control unit. The ACC control unit is switched off at a vehicle voltage greater than 16 V in order to protect the processor. The lens heating is monitored by the ACC control unit for faults.