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Engine off energy management, function - GF54.10-P-1050CA

MODEL 207.3/4 up to model year 2014 

Function requirements, general 

IMPORTANT The CDI control unit (N3/9) (with diesel engine) or the ME-SFI control unit (N3/10) (with gasoline engine) sends the "Engine running" or "Drivetrain operational" signal via the chassis CAN (CAN E), front SAM control unit with fuse and relay module (N10/1) and interior CAN (CAN B) to the rear SAM control unit with fuse and relay module (N10/2).

Engine off energy management, general 

Engine off energy management ensures the stability of the on-board electrical system and the starting capability of the engine when the vehicle is parked.

This functionality is integrated into the rear SAM control unit and serves to extend the service life of the on-board electrical system battery (G1). To this end, active electrical consumers may be switched off.

Engine OFF energy management encompasses the following subfunctions:

Additional function requirements for consumer reduction (deactivation of comfort functions) 

IMPORTANT The electronic ignition lock control unit (N73) transmits the circuit status of circuit 15 via the interior CAN to the rear SAM control unit.

Function sequence for consumer reduction (deactivation of convenience functions) 

If the on-board electrical system voltage drops below U = 11.8 V for t = 5 s, the rear SAM control unit activates the consumer reduction function (deactivation of comfort functions) and sends the request to reduce the power consumption of consumers or to deactivate consumers via the interior CAN to the corresponding control units. Given constant shutoff conditions, one consumer will be shut off every t = 5 s in addition to the consumer reduction from the engine on energy management function.

The shutoff sequence is shown in the table below.

IMPORTANT The list includes those consumers whose power supply is reduced or cutoff as part of the engine ON energy management function (up to shutoff step 14).

Shutoff step Shutoff stage Power-reduced or deactivated function Executing control unit Maximum current in A
1 1 Heating level 6, heat boosting (with engine 271.8, 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
2 2 Heating level 5, heat boosting (with engine 271.8, 642.8, 651.9), driver side Automatic climate control and operating unit (N22/7) 18.5
3 3 Heating level 4, heat boosting (with engine 271.8, 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
4 4 Heating level 3, heat boosting (with engine 271.8, 642.8, 651.9), driver side Automatic climate control and operating unit (N22/7) 18.5
5 5 Heating level 2, heat boosting (with engine 271.8, 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
6 6 Heating level 1, heat boosting (with engine 271.8, 642.8, 651.9), driver side Automatic climate control and operating unit (N22/7) 18.5
7 7 Seat heater level 3 (with code (873) Seat heater for left and right front seats) Rear SAM control unit with fuse and relay module (N10/2) 13.2
8 8 Seat heater level 2 (with code (873) Seat heater for left and right front seats) Rear SAM control unit with fuse and relay module (N10/2) 13.2
9 10 Mirror heater Left front door control unit (N69/1) and right front door control unit (N69/2) 3.5
10 12 Rear window heater Rear SAM control unit with fuse and relay module (N10/2) 30.0
11 14 Interior blower P = 50 % Automatic climate control and operating unit (N22/7) 16.0
12 15 Cooling fan P = 50 % Automatic climate control and operating unit (N22/7) 31.0
13 16 Circuit 15R relay (1) (N10/2kB) Rear SAM control unit with fuse and relay module (N10/2) 6
14 18 Seat heater stage 1 (with code (873) Seat heater for left and right front seats) Rear SAM control unit with fuse and relay module (N10/2) 3.3
15 19 Residual heat utilization (with code (581) Comfort automatic air conditioning and without code (494) USA version) Automatic climate control and operating unit (N22/7) 8
16 20 Stationary heater (with code (228) Stationary heater) Stationary heater control unit (A6n1) 10
17 21 Audio system Radio (A2) (with code (510) Audio 20 with CD changer or code (523) MB Audio 20 radio) or Radio with auto pilot system (A2/56) (with code (511) Audio 50 APS incl. DVD changer or code (525) MB Audio 50 APS radio) or COMAND controller unit (A40/3) (with code (512) COMAND APS incl. DVD changer or code (527) COMAND APS with single DVD drive (with navigation) or code (528) COMAND incl. DVD changer) 2

The shutoff sequence is shown up to 31.5.12 in the table below.

IMPORTANT The list includes those consumers whose power supply is reduced or shut off as part of the engine ON energy management function (up to shutoff step 16).

Shutoff step Shutoff stage Power-reduced or deactivated function Executing control unit Maximum current in A
1 1 Heating level 6, heat boosting (with engine 271.8, 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
2 2 Heating level 5, heat boosting (with engine 271.8, 642.8, 651.9), driver side Automatic climate control and operating unit (N22/7) 18.5
3 3 Heating level 4, heat boosting (with engine 271.8, 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
4 4 Heating level 3, heat boosting (with engine 271.8, 642.8, 651.9), driver side Automatic climate control and operating unit (N22/7) 18.5
5 5 Heating level 2, heat boosting (with engine 271.8, 642.8, 651.9), passenger side Automatic climate control and operating unit (N22/7) 18.5
6 6 Heating level 1, heat boosting (with engine 271.8, 642.8, 651.9), driver side Automatic climate control and operating unit (N22/7) 18.5
7 8 Interior blower P = 50 % Automatic climate control and operating unit (N22/7) 16.0
8 9 Cooling fan P = 50 % Automatic climate control and operating unit (N22/7) 31.0
9 10 Trailer lighting system (with code (550) Trailer hitch) Trailer recognition control unit (N28/1) (with code (550) Trailer hitch) 8
10 11 Circuit 15R relay (1) (N10/2kB) Rear SAM control unit with fuse and relay module (N10/2) 6
11 12 Seat ventilation (with code (401) Front comfort seats, incl. seat heating and seat ventilation) Rear SAM control unit with fuse and relay module (N10/2) 2.2
12 13 Seat heater level 3 (with code (873) Seat heater for left and right front seats) Rear SAM control unit with fuse and relay module (N10/2) 13.2
13 14 Rear window heater Rear SAM control unit with fuse and relay module (N10/2) 30.0
14 16 Seat heater level 2 (with code (873) Seat heater for left and right front seats) Rear SAM control unit with fuse and relay module (N10/2) 13.2
15 17 Seat heater stage 1 (with code (873) Seat heater for left and right front seats) Rear SAM control unit with fuse and relay module (N10/2) 3.3
16 20 Mirror heater Left front door control unit (N69/1) and right front door control unit (N69/2) 3.5
17 21 Residual heat utilization (with code (581) Comfort automatic air conditioning and without code (494) USA version) Automatic climate control and operating unit (N22/7) 8
18 22 Comfort lamps Front SAM control unit with fuse and relay module (N10/1) 1
    Trunk illumination, interior illumination Rear SAM control unit with fuse and relay module (N10/2) 0.5
19 24 Stationary heater (with code (228) Stationary heater) Stationary heater control unit (A6n1) 10
20 25 Audio system Radio (A2) (with code (510) Audio 20 with CD changer or code (523) MB Audio 20 radio) or Radio with auto pilot system (A2/56) (with code (511) Audio 50 APS incl. DVD changer or code (525) MB Audio 50 APS radio) or COMAND controller unit (A40/3) (with code (512) COMAND APS incl. DVD changer or code (527) COMAND APS with single DVD drive (with navigation) or code (528) COMAND incl. DVD changer) 2

The consumer shutoff is not canceled even if the on-board electrical system voltage stabilizes at a value above U = 11.8 V. The switched-off consumers are switched on again only after Circuit 15C ON has been reset.

Additional function requirements for no-load current management 

IMPORTANT The electronic ignition lock control unit sends the circuit 15 status over the interior CAN to the rear SAM control unit.

Function sequence for no-load current management 

No-load current management ensures the engine's starting capability even after extended idle times. No-load current management is integrated into the rear SAM control unit.

Actuation of the no-load current shutoff relay (F32k2) in the front prefuse box (F32) shuts off consumers that are supplied with power via circuit 30g.

No-load current management however, can accommodate increased power consumption for a specific period after switching off the engine (maximum t = 75 min.). This allows, for example, the radio to be played while the car is being washed.

No-load current management cyclically measures the voltage and power consumption every t = 6 minutes. If an excessively high no-load current is determined for a specific period, the no-load current shutoff relay is opened at the earliest after t = 75 min, but no later than t = 6 h.

Following a period of t = 6 h, or as soon as the on-board electrical system's voltage values drop below certain limits and compromise the engine's starting capability, the extended run-on monitoring function initiates the following actions:

Before opening the no-load current switch relay a corresponding signal is sent over the CAN to shutdown the control units. This also causes, for example, the panoramic sliding sunroof control unit (A98n1) (with code (413) Panoramic glass sunroof with top sliding sunroof) to move an open panoramic sliding sunroof to the tilt position.

The no-load current management system comprises the following subfunctions:

Function sequence for no-load current shutoff 

The no-load current shutoff system comprises the following subfunctions:

Function sequence for requesting consumer shutoff (no-load current switch) 

During the transition from circuit 15R to circuit 15C, the vehicle changes to the "vehicle rest" operating state.

The timer counting down to no-load current shutoff is then started (waiting time t = 6 h). The no-load current is continuously monitored by the battery sensor (B95). If the no-load current is too high, the no-load current shutoff relay will be opened at the earliest after t = 75 minutes. The rear SAM control unit reads in the data from the battery sensor over the on-board electrical system LIN (LIN B7) and evaluates it.

If the on-board electrical system voltage drops within the waiting time to U < 11.8 V, the no-load current shutoff relay is prematurely opened.

IMPORTANT If U < 11.8 V, the battery sensor will go into sleep mode (reduced power consumption).

At t = 5 min before the no-load current shutoff relay is opened, the rear SAM control unit sends a shutoff signal as advance notice to all control units supplied with power via circuit 30g. The rear SAM control unit transmits this cutoff signal via interior CAN.

The following control units receive the shutoff signal via the interior CAN:

The radio or the COMAND controller unit sends the shutoff signal via the telematics CAN (CAN A) and Media Oriented System Transport (MOST).

The following control units receive the shutoff signal via the telematics CAN:

The following control units receive the shutoff signal via MOST:

The front SAM control unit sends the shutoff signal via the chassis CAN.

The following control units receive the shutoff signal over the chassis CAN:

If a CAN is in "sleep mode" during signal transmission, the corresponding control units are woken up. The control units will then prepare themselves for power supply shutoff. Within t = 5 min., these control units will go into "power-down mode" (decentralized power management).

Function sequence for shut off consumers 

Following a period of t = 5 min., no-load current management opens the no-load current shutoff relay provided no closing causing event has occurred in the meantime. For this purpose, the rear SAM control unit actuates the no-load current shutoff relay directly. The rear SAM control unit then sends the switching status of the no-load current shutoff relay via the interior CAN to the corresponding control units.

IMPORTANT Detailed information on the signal flow is given in the chapter "Requesting consumer shutoff (no-load current switch)".

Function sequence for energize consumers 

The no-load current management closes the no-load current shutoff relay as soon as a system is activated. All the functions are then available again. The no-load current shutoff relay is opened again when the waiting time of t = 6 h has expired, the on-board electrical system voltage is less than U = 11.8 V or the no-load current is too high.

If the rear SAM control unit receives a wake-up signal, no-load current management closes the no-load current shutoff relay and signals, via the interior CAN, that the wake-up conditions for the control units are again active. Closing the no-load current shutoff relay causes power to again be supplied via circuit 30g.

IMPORTANT Detailed information on the signal flow is given in the chapter "Requesting consumer shutoff (no-load current switch)".

The following conditions will trigger the closure of the no-load current shutoff relay:

Function sequence for no-load current diagnosis 

No-load current diagnosis records data to help troubleshoot possible fault profiles.

The no-load current diagnosis comprises the following subfunctions:

Additional function requirements for Activate no-load current diagnosis 

Function sequence for activate no-load current diagnosis 

The battery sensor starts the no-load current diagnosis over the on-board electrical system LIN if one of the following events occurs:

With the first waking event an entry in the no-load current fault roll takes place. Following this, the no-load current is cyclically checked. These values will be updated if there are significant changes or if the no-load current diagnosis is canceled.

The following data are stored in nonvolatile memory in the no-load current fault roll:

As long as no-load current diagnosis is active, each additional battery sensor wake-up event will cause the data record to be updated.

Additional function requirements for cancel/end no-load current diagnosis 

Function sequence for cancel/end no-load current diagnosis 

The no-load current diagnosis is canceled when the limit value (U < 11.8 V) for the on-board electrical system voltage is undershot. The battery sensor will discontinue no-load current monitoring in order to minimize electricity consumption. Once this happens, no further entries will be added to the quiescent current fault roll.

Additional function requirements for no-load current reference value/residual charging current assessment 

No-load current reference value/residual charging current assessment function sequence 

After the vehicle has gone through production testing and possible runs on the test track, the no-load current has to be measured and an assessment made of the residual charge current of the on-board electrical system battery.

The no-load current reference value/residual charging current evaluation function comprises the following subfunctions:

No-load current reference value measurement function sequence 

The measurement of the no-load current reference value is started using the diagnostic-tester at circuit 15R or higher. The message "Measure no-load current (A1p13)" appears in the multifunction display of the IC (A1). The request for this is sent by the rear SAM control unit via the interior CAN to the instrument cluster. The diagnostic tester must then be removed and the vehicle locked so that the vehicle's no-load current will quickly drop. The battery sensor will then sense and save the maximum no-load current level to occur following the locking of the vehicle. After the vehicle is woken up, the battery sensor sends the measured no-load current value via the on-board electrical system LIN to the rear SAM control unit, which then saves it as the no-load current reference value in nonvolatile memory. The no-load current reference value can be read out using the diagnostic tester.

IMPORTANT If the measured no-load current is within a defined tolerance range, the message in the multifunction display will disappear. If the no-load current reference value is too high, a fault message will be shown in the multifunction display of the instrument cluster and measurement will begin again.

Function sequence for residual charge current assessment 

During production, charge is removed from the battery in the course of various function tests. The charge level of the on-board electrical system battery must therefore be assessed at the end of assembly. The charge level (ratio of current charge to the maximum storable charge) serves as the measure for a sufficiently charged on-board electrical system battery. This value must be above 80%. If the charge level is below 80%, a fault message will be shown in the multifunction display of the instrument cluster. The request for this is sent by the rear SAM control unit via the interior CAN to the instrument cluster. Measurement of the residual charge current is only done following successful measurement of the no-load current reference value. As a rule, the two values are released together.

Function sequence for remote charging/jump start 

If the on-board electrical system battery does not have enough capacity to start the engine, the on-board electrical system battery must be charged or a jump start carried out.

IMPORTANT As of 1.6.10, one of the front doors must be opened during a jump start procedure or during any testing in the workshop to enable the alternator management to change to the jump starting mode or the workshop mode and the alternator voltage to be increased to U = 14.3 V.

  Electrical function schematic for no-load current management   PE54.10-P-2074-97EAA
  Electrical function schematic for comfort function shutoff   PE54.10-P-2076-97EAA
  Overview of energy management system components   GF54.10-P-9990CA 
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