On-board electrical system emergency mode function - GF54.10-P-2001CW

MODEL 204.0/2 up to Model Year 2008 

Function requirements: 

• Engine running (circuit 61 ON)

On-board electrical system emergency mode, in general 

The rear SAM control unit with fuse and relay module (N10/2) actuates the on-board electrical system emergency mode to match the permissible voltage of the on-board electrical system battery (G1).

The following functions can be authorized:

• Activate on-board electrical system emergency mode
  • Idle speed increase
  • Deactivation of alternator management
  • Consumer shutoff
• Deactivate on-board electrical system emergency mode

Activate on-board electrical system emergency mode 

Additional function prerequisites 

• The on-board electrical system battery voltage is U ≤ 10.8 V for t ≥ 10 s

The voltage level is determined by the battery sensor (B95) and evaluated by the rear SAM control unit.

Activate on-board electrical system emergency mode function sequence 

If the permissible voltage is dropped below, the rear SAM control unit signals the on-board electrical system emergency mode to the interior CAN and over the front SAM control unit with fuse and relay module (N10/1) on the chassis CAN. The following functions are then activated:

Idle speed increase:

The rear SAM control unit sends the request over the front SAM control unit to the ME-SFI [ME] control unit (N3/10) (for gasoline engines) or the CDI control unit (N3/9) (for diesel engines). The ME-SFI [ME] control unit or the CDI control unit increases the idle speed, but it does not do so until the engine speed n > 900 rpm. The increased idle speed enables a higher alternator (G2) power output to be achieved.

The idle speed increase is also actuated, if point 2 of the consumer shutoff is active.

The idle speed increase is reset at:

• Engine off or alternator defective
• Simultaneous presence of the following conditions:
  • Consumer shutoff inactive
  • On-board electrical system emergency mode active

Deactivation of alternator management:

The rear SAM control unit transmits the request over the front SAM control unit to the ME-SFI [ME] control unit or the CDI control unit. The ME-SFI [ME] control unit or the CDI control unit increases the alternator's excitation current, so that it can then make its full power available.

Consumer shutoff:

The consumer shutoff requests are issued successively with a cycle time of t = 200 ms from the rear SAM control unit over the interior CAN.

The following consumers have their output reduced or switched off in the specified sequence:

1. The heater stages of the PTC heater booster (R22/3) (three each on driver and front passenger sides) are switched off alternately, one after the other, starting with the front passenger-side, by the automatic air conditioning control and operating unit (N22/7) (diesel engine only).
2. The automatic air conditioning control and operating unit reduces actuation of the rear blower motor (M2/1) to 50 % (with code (581) Comfort automatic air conditioning).
3. The automatic air conditioning control and operating unit reduces actuation of the blower motor (A32m1) to 50 %.
4. The automatic air conditioning control and operating unit reduces actuation of the fan motor control unit (N65/2) to 50 %.
5. Deactivation of trailer socket (X58) by rear SAM control unit (with code (550) Trailer hitch).
6. Deactivation of heating stage 3 of seat heater by rear SAM control unit (with code (873) Right and left front seat heaters).
7. Deactivation of rear window heater (R1) by rear SAM control unit.
8. Gradual deactivation of heater stages 2 and 1 of seat heater by rear SAM control unit (with code (873) Right and left front seat heaters).
9. Deactivation of mirror heater (M21/1r1) by left front-door control unit (N69/1) and deactivation of mirror heater (M21/2r1) by right front-door control unit (N69/2).
10. Deactivation of residual engine heat utilization function by the automatic air conditioning control and operating unit (with code (581) Comfort automatic air conditioning, not).
11. Deactivation of rear automatic air conditioning operating unit (N22/4) by automatic air conditioning control and operating unit (with code (581) Comfort automatic air conditioning).
12. Deactivation of interior illumination by front SAM control unit.
13. Deactivation of roof sign, printer, card reader by special-purpose vehicle multifunction control unit (N26/9) (for special-purpose vehicles).
14. Deactivation of all audio components by radio (A2), by radio with auto pilot system (A2/56) or from the COMAND controller unit (A40/3).

At the same time, with code (299) PRE-SAFE the left front reversible emergency tensioning retractor (A76) and right front reversible emergency tensioning retractor (A76/1) are deactivated.

Deactivate on-board electrical system emergency mode 

Additional function prerequisites 

• Voltage of on-board electrical system battery U > 10.8 V for t ≥ 10 s

Deactivate on-board electrical system emergency mode function sequence 

When the function requirements are fulfilled, the rear SAM control unit terminates the on-board electrical system emergency mode as follows:

• The idle speed increase is reset by the rear SAM control unit, the actual lowering of the idle speed does not take place until the engine is restarted.
• The switched-off consumers are activated again when the next ignition sequence (as of circuit 15R ON) is executed.

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