Current Limitation

Current limitation - Central electronic module (CEM)

Current limiting




The central electronic module (CEM) (4/56) communicates with the engine control module (ECM) (4/46) via CAN. The engine control module (ECM) in turn communicates with the alternator control module (ACM) (4/98) via LIN communication. Thus, the central electronic module (CEM) receives information on how much current is produced by the alternator and how much can be used for various loads in the vehicle.
Under certain conditions, the alternator cannot produce enough current for the connected loads. The central electronic module (CEM) communicates with the climate control module (CCM) (4/6), which then completely or partially switches off the following loads:
- electrical additional heater
- rear demist
- electrically heated seats
- heated door mirrors.
The central electronic module (CEM) also transmits a request via the Control area network (CAN) to the engine control module (ECM) to increase the engine idle speed.
When the engine is not running all current is taken from the battery. There are a number of different loads which can be activated when the engine is not running, for example the infotainment system. The central electronic module (CEM) continuously monitors the voltage level of the battery. When the voltage level is too low the central electronic module (CEM) transmits information to the infotainment control module (ICM) (3/281) which then shuts off the infotainment system. In the event of a fault, the central electronic module (CEM) transmits data via the Control area network (CAN) to the driver information module (DIM) (5/1) which displays a text message to the user.
If the infotainment system used in ignition position II when the engine is not running, information is sent to the driver information module (DIM). A message is displayed to inform the user that the entire infotainment system will be shut off in 2 minutes.
Charge voltage
In order to charge the battery optimally, the central electronic module (CEM) calculates output voltage from the alternator based on battery temperature. The alternator control module (ACM) (charge regulator) will then regulate output voltage based on control from the central electronic module (CEM). As the engine control module (ECM) can also control the alternator, there may be output voltages deviations, such as in different driving situations.