On-board computer control, function - GF54.10-P-0002CW

MODEL 204.0/2 up to Model Year 2008 

On-board computer control, general 

The on-board computer control is integrated into the rear SAM control unit with fuse and relay module (N10/2) and its task is to ensure that the supply meets given demand and situations relevant to all electrical consumers and to safeguard the vehicle's starting capability.

The system consists of an alternator (G2) for the power supply, the on-board electrical system battery (G1) for storing power or the power supply when the engine is off and all the electrical components whose performance influences the on-board electrical system.

The on-board electrical system battery is used to provide the electrical consumers with power when the vehicle is in a state of rest.

The state of the on-board electrical system battery is monitored by the battery sensor (B95). The voltage, current and temperature measurements enable the battery sensor to calculate parameters, which then serve as the basis for the on-board computer control. Based on the battery temperature and voltage level of the on-board electrical system battery, the alternator's nominal voltage is also called on to calculate the ideal charging voltage, whereupon it is then sent to the ME-SFI [ME] control unit (N3/10) (for gasoline engines) or to the CDI control unit (N3/9) (for diesel engines).

The ME-SFI [ME] control unit or the CDI control unit forwards the specified values to the alternator or the alternator management sets limits on the controlled speed or permanent voltage values to match the vehicle status taking the boundary conditions (such as, e.g. optimization of exhaust, consumption, comfort).

The on-board computer control enables the following subfunctions to be performed: 

• Normal mode

Also still possible are the following functions, which are described separately in the corresponding subfunctions:

• Vehicle standby
• On-board electrical system emergency running mode
• Consumer shutoff

Normal mode 

From circuit 15R ON the on-board computer control is in normal mode. The quiescent current cutout relay (F32k2) is closed. Engine operation (circuit 61 ON) is detected over the chassis CAN by the ME-SFI [ME] control unit or the CDI control unit.

During normal mode, the battery sensor detects the battery parameters. These are then used by the on-board computer control in the rear SAM control unit to calculate the alternator's specified voltage, to provide the on-board electrical system battery with sufficient charging current.

	On-board computer control, location of components		GF54.10-P-0002-01CW
	On-board computer control, block diagram		GF54.10-P-0002-02CW
	Vehicle idle function		GF54.10-P-2000CW
	On-board electrical system emergency mode function		GF54.10-P-2001CW
	Consumer shutoff function		GF54.10-P-2002CW