Transfer case control, function - GF28.19-P-3000GA

MODEL 463.244 /245 /247 /248 /249 /250 /254 /303 /309 /322 /323 /332 /333 /340 /341 up to 31.8.08 with TRANSFER CASE 750.654

Fig 1: Transfer Case Control Function Diagram

Courtesy of MERCEDES-BENZ USA

The VGS [fully integrated transmission control] control unit (N15/7) controls the complete shift operations of the transfer case by means of a special software:

Receiving, evaluating and passing on the shift requirement

Depending on the three possible shift conditions ("LOW", "NEUTRAL", "HIGH") of the transfer case switch (S97/5) the VGS control unit (N15/7) receives an analog input signal via a discrete line.

After the VGS control unit (N15/7) has recorded and evaluated the operating condition of the transfer case, the electromotive shift mechanism is initiated by actuation of the transfer case actuator motor (M46/2) by means of an analog shift signal.

Recording and evaluating the operating condition of the transfer case

The VGS control unit (N15/7) evaluates the current operating condition of the transfer case and in this way checks whether the preconditions for a shift are met.

The data required for this are made available as digital input signals from the following control units:

ME-SFI control unit (N3/10) or CDI control unit (N39/2)
ABS control unit (N47-7)
ETC control unit (N15/3)
Electronic selector lever module control unit (N15/5)
Instrument cluster (A1)

A Hall sensor integrated in the transfer case actuator motor (M46/2) supplies via a rotation angle output and a direction output pulses to the VGS N15/7), which correspond to the rotation angle and direction of rotation of the rotor. Together with the default position ("LOW", "NEUTRAL", "HIGH" stored in the VGS control unit (N15/7) this calculates the current position (rotation angle and direction of rotation) of the transfer case actuator motor (M46/2).

The transfer case engagement indicator indicates the shift condition of the transfer case.

Storage of data

During each shift operation the current shift position is stored cyclically in the memory of the VGS control unit (N15/7). This shift position is defined as the default position for the next shift operation.
Force-optimized and distance-optimized characteristics stored in the memory determine the actual signal for the transfer case actuator motor (M46/2).
In the event of operating faults, operating errors or impermissible shift commands, stored, logical shift programs take over the shift operation (see special cases of control).
Storage of fault codes which can be read out via the data link connector (X11/4).

Special cases of control

After an aborted shift attempt a second shift attempt into the selected gear takes place through the shift logic of the VGS control unit(N15/7 If this shift attempt again leads to an incomplete shift, the transmission shifts down into the gear last engaged.
If in turn this downshift leads to an incomplete shift, the shift collar moves into neutral and an acoustic and optical signal makes the driver aware that no gear in the transfer case is engaged.
If due to another problem no gear can be engaged or the shift collar moves into neutral and no further shift operation is initiated by the VGS control unit (N15/7) (exception: towing), an acoustic and optical signal makes the driver aware that no gear in the transfer case is engaged.
If the ignition is switched off during the shift operation, the shift operation is continued until it is completed. However if in this case the shift operation leads to an incomplete shift, then a downshift into the gear last engaged is initiated by the VGS control unit VGS (N15/7). If in turn this operation leads to an incomplete shift then the shift collar moves into neutral and an acoustic and optical signal makes the driver aware that no gear in the transfer case is engaged.
At a standstill and simultaneous selector lever position "P" the software ensures that either the on-road gear or the off-road gear of the transfer case is engaged. If it is not possible and no gear is engaged then attention to this is drawn by an acoustic and optical signal
In the event of loss of the shift position it is possible to continue a shift provided that no mechanical and electrical damage exist. If during further shift operations it is found by a comparison of shift travels before and after the loss of the shift position that these travels are the same size (within a certain tolerance limit), the fault stored in the VGS control unit (N15/7) is marked as not active.
Each time after the engine is started the position stored in the VGS control unit (N15/7) is checked and re-adjusted when the neutral stage is engaged for the first time.

Voltage supply

The VGS control unit (N15/7) receives its supply voltage

via circuit 30 (fuse 39 (F34f39) in the interior fuse box) and
via circuit 15 (front SAM signal acquisition and actuation module (N10/1), connector 9 Pin 2)

	Transfer case switch, location/task		GF28.19-P-3101GA
	Transfer case engagement indicator, location/task		GF28.19-P-3102GA
	Transfer case control unit, location/task		GF28.19-P-3103GA
	Transfer case electric actuator motor, location/task/design/function		GF28.19-P-3400GA