Normal operation of 2-battery on-board electrical system, function - GF54.10-P-1101SX

MODEL 216.3, 221.0 /1 up to Model Year 8

Normal operation, shown on running engine

Fig 1: Identifying Normal Operation Of 2-Battery On-Board Electrical System Function Chart

Courtesy of MERCEDES-BENZ USA

Engine start

Both the battery circuits are separated from each other electrically during the starting process. The on-board electrical system is supplied by the supply battery circuit. The starter battery circuit guarantees that the vehicle is started.

Vehicles with diesel engine:

If the engine oil temperature drops below the value of -10 °C, the vehicle power supply control unit actuates the battery-coupling relay (F32k1) in the case of circuit 50 ON or preglowing in order to connect the starter battery and the on-board electrical system battery in parallel.

As soon as the "engine running" signal is applied for 30 s, the battery coupling relay is opened again.

Engine "ON"

If the engine is running, the starter battery is also recharged even if the on-board power supply voltage is low. As long as the engine is running, the charge converter regulates recharging of the starter battery to the specified charging voltage according to a temperature-controlled charging characteristic initiated by the vehicle power supply control unit.

The charge level of the two batteries is influenced by various algorithms, i.e. if both batteries are fully charged, the charging current is limited by the alternator in order to optimize consumption (fuel) and to improve the efficiency of the engine.

Consumer shutoff:

There are situations in which consumers have to be switched off in order to sufficiently recharge the on-board electrical system battery and to ensure a stable power supply to all important components. Certain consumers are switched off temporarily at short notice in a defined sequence.

The idle speed can also be increased in order to allow the alternator to increase its power output. The idle speed is increased via the CDI control unit or ME-SFI [ME] control unit.

Consumer shutoff with engine "ON"

If the voltage drops below 12.2 V for longer than 2 s, the first consumer is switched off. If the voltage does not increase, a further consumer is switched off every second.

The request to switch off the consumers is sent from the vehicle power supply control unit via the central gateway control unit on the interior CAN. The consumers and functions are then deactivated by the associated control unit.

Omission of air-conditioning request for engine and air-conditioning electric suction fan with integrated control (M4/7)
Trailer hitch socket (13-pin) (X58), circuit 30
Front cigar lighter with ashtray illumination (R3), power outlets etc.
Seat heater stage 3
Heated rear window
Wiper rest heater

Shutoff sequence (depends on equipment installed)

Stage 3 (passenger-side) of PTC heater booster (R22/3) heating element
Stage 3 (driver-side) of PTC heater booster heating element
Stage 2 (passenger-side) of PTC heater booster heating element
Stage 2 (driver-side) of PTC heater booster heating element
Stage 1 (passenger-side) of PTC heater booster heating element
Stage 1 (driver-side) of PTC heater booster heating element
Rear blower motor (M2/1) is reduced to 50 %
Blower motor (A32m1) is reduced to 50 %
Seat heater stage 2
Seat heater stage 1
Heated steering wheel
Heated windshield
Mirror heater

The consumer shutoff starts from the beginning again with the operating condition "engine ON", irrespective of whether consumer shutoff was already active with the operating condition "engine OFF".

Consumer shutoff with engine "OFF"

If electrical functions continue to be required for circuit 15 or circuit 15R, the consumer shutoff intervenes as soon as the on-board power supply voltage drops below a programmed voltage value. The consumers are then switched off in a certain sequence at certain intervals.

If the on-board power supply voltage drops below a value of 11.8 V over a period longer than 10 s or no CAN communication takes place for over 6 h, the quiescent current cutout relay opens and the following consumers (circuit 30g) are switched off:

Left instrument panel fuse box (F1/7)
Front SAM control unit with fuse and relay module (N10/1)
Rear SAM control unit with fuse and relay module (N10/2)

If the bus idle state exists, the vehicle power supply control unit also enters the idle state even if the quiescent current cutout relay is closed.

If an on-board power supply voltage of 11.5 V exists for longer than 60 s, consumers are switched off in stages with a delay of 60 s in each case.

Shutoff sequence (depends on equipment installed)

Wiper rest heater
Seat ventilation
Seat heater stage 3
Rear backrest refrigerator box (A39/1)
Rear blower motor is reduced to 50 %
Blower motor is reduced to 50 %
Electric suction fan for engine and air-conditioning system is reduced to 50 %
Seat heater stage 2
Seat heater stage 1
Heated rear window
Heated steering wheel
COMAND controller unit (A40/3)
Trailer hitch socket (13-pin)
Luggage compartment socket (X58/12), front cigar lighter with ashtray illumination, rear cigar lighter (R3/1)
Roof sign, printer, card reader
Interior illumination

CDI control unit component description	N3/9 Model 221 with engine 642	GF07.16-P-6000SX
ME-SFI control unit, location/task/design/function	N3/10 Model 221 with engine 275.953/982	GF07.61-P-5000M
ME-SFI [ME] control unit, component description	N3/10 Model 221 with engine 272.965, 273.961 Model 216 with engine 273.961	GF07.61-P-6000V
Vehicle power supply control unit, component description	N82/1	GF54.21-P-4126SX
Central gateway control unit, component description	N93	GF54.21-P-4170SX