Transfer Case (VG), Function - GF28.10-D-0002TSC

Model 907 

with code ZG1 (Engageable all-wheel drive) 

except code ZG3 (Engageable all-wheel drive with gear reduction) 

General 

On vehicles with code ZG1 (All-wheel drive, engageable), an engageable all-wheel drive with a planetary gear set (in transfer case) and 2 open differentials (in rear and front axle) is used. When the all-wheel drive is engaged the torque distribution between the front and rear axle is permanently set by the planetary gear set at 33 % to the front axle and 67 % to the rear axle.

What makes this so special is that there are no mechanical longitudinal and transverse differential locks. Instead, the all-wheel drive operates together with the Electronic Stability Program (ESP®) that is specifically tuned to the all-wheel drive.

The ESP® is automatically switched on when one or more wheels start to spin on slippery ground. When this happens, it selectively brakes the spinning wheel or the spinning wheels or it influences the engine torque. This simultaneously increases the drive torque at those wheels that still have sufficient road grip. Automatic brake application by the ESP® can simulate the effect provided by up to 3 differential locks.

The engageable all-wheel drive enables the number of driven wheels and therefore the degree of road adhesion to be improved. As a result, slip is reduced and the driving power is distributed to all of the wheels.

The distributed driving power results in higher traction and higher lateral stability at the wheels.

Function requirements for successful engagement of all-wheel drive 

The following requirements must be satisfied:

• Circuit 15 ON
• Vehicle speed below 14 km/h; as of 14 km/h, the activation must be completed.
• Switch-on signal of all-wheel drive activation button (S76/11)
• ESP® not operating.
• Engine torque below defined limit value.

Engagement of all-wheel drive, function 

During activation, the light-emitting diode (LED) in the all-wheel drive activation button flashes and the indicator lamps for the ESP® as well as acceleration skid control (ASR) light up in the display.

If the all-wheel drive is switched on successfully, the LED in the all-wheel drive activation button lights up permanently and the indicator lamps in the display for the ESP® as well as ASR go out.

If all-wheel drive cannot be engaged, the LED in the all-wheel drive activation button flashes 3 times.

ASR and ESP® are not available during all-wheel drive activation. ABS is available.

At "circuit 15 OFF", the all-wheel drive is switched off.

If, owing to the gear position in the transfer case, it is not possible to immediately activate the all-wheel drive, the respective sliding sleeve is pre-compressed by the torsion spring in the worm gear of the transfer case actuator motor (M46/2), by the selector drum and the corresponding shift fork. This means that the all-wheel drive can be activated at the next gear wheel rotation.

Possible faults in the all-wheel drive system are stored in the ESP® control unit (N30/4) and they can be read out there using XENTRY Diagnosis.

Transfer case (VG), power flow	GF28.10-D-0002-05TSC
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