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Gear Shift, Function - GF27.60-P-2000ANG

Transmission 725.0 (except 725.017) in model 205 

Function requirements, general 

IMPORTANT The CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine) sends the status of the engine management, the "Engine running" signal and the engine speed over the drive CAN (CAN C1) to the fully integrated transmission control unit (Y3/8n4).

The Electronic Stability Program control unit (N30/4) sends the vehicle speed over the suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN to the fully integrated transmission control unit.

Shift operation, general 

The fully integrated transmission control performs all shift operations and drive range changes. Gear ranges "P", "R", "N", "D" are selected using the DIRECT SELECT lever (S16/13) located on the right of the steering column tube module. The steering column tube module control unit (N80) directly reads in the shift positions of the DIRECT SELECT lever and transmits these via the suspension FlexRay, powertrain control unit and drive CAN to the fully integrated transmission control unit.

IMPORTANTMessages and displays in instrument cluster (A1) 

Information on the selected gear, the engaged gear range and the transmission mode is sent by the fully integrated transmission control unit via the drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit (N73) and user interface CAN (CAN HMI) to the instrument cluster. The instrument cluster then actuates the relevant displays.

The fully integrated transmission control unit processes the signals for the following components:

The following component parts are actuated by the fully integrated transmission control unit:

The following data is exchanged between the fully integrated transmission control unit and the CDI control unit or ME-SFI [ME] control unit via the drive train CAN:

Upshifting and downshifting 

Pressing the steering wheel upshift button (S111/1) shifts up a gear. Pressing the steering wheel downshift button (S110/1) shifts down a gear. During an active drive program, the short-term M program is activated.

At the same time, the shift range is extended or limited in drive programs "E", "S" and "S+". If the steering wheel upshift button is pressed and held, the gear range changes from "D1" to "D9". If the steering wheel downshift button is pressed and held, a shift is made to a shift range in which the vehicle can be more easily accelerated or braked.

IMPORTANTShort-term M program 

The short-term M program is a temporary mode that is activated when the steering wheel gearshift buttons are operated. When one of the steering wheel gearshift buttons is operated, the transmission control switches up or down a gear, if it is allowed. Otherwise, the current gear is maintained. The short-term M mode is deactivated after expiration of a defined period. This period can be extended by dropping below a minimum speed (e.g. stopping), upon recognition of lateral acceleration or if the vehicle is in overrun mode. The driver can personally interrupt the short-term M program prematurely with certain actions. For example, pressing and holding the steering wheel upshift button or changing drive range or drive program.

The driver can use the DYNAMIC SELECT switch (N72/4s11) in the left lower control panel (N72/4) to select different drive programs. The basic shift program is influenced accordingly.

The left lower control panel sends the status of the DYNAMIC SELECT switch over the LCP-LIN (LIN A3), Audio/COMAND control panel (A40/9) (except code 446 (Touchpad only) or touchpad (A105) (with code 446 (Touchpad only)), telematics CAN (CAN A), head unit (A26/17), user interface CAN, electronic ignition lock control unit and the suspension FlexRay to the Electronic Stability Program control unit. The Electronic Stability Program control unit transmits information on the selected drive program via the suspension FlexRay, powertrain control unit and drive CAN to the fully integrated transmission control unit.

The reverse gear and neutral gear can only be shifted to using the DIRECT SELECT lever. The park pawl (gear range "P") is activated by operating the park pawl on the DIRECT SELECT lever.

The steering wheel electronics (N135) read in the status of the steering wheel gearshift buttons directly and sends this over the steering LIN (LIN E1) (up to model year 2019) or over the steering wheel CAN (CAN LR) (as of model year 2019), steering column tube module control unit, suspension FlexRay, powertrain control unit and drive CAN to the fully integrated transmission control unit.

Shift operation 1 to 2 

Multidisk brake B05, multidisk brake B06 and multidisk clutch K38 are engaged in 1st gear. When shifting from 1st gear to 2nd gear, multidisk brake B05 is disengaged and multidisk clutch K81 is engaged. The shift operation is started by the fully integrated transmission control unit. The multidisk brake B08 is filled and the pressure in the multidisk brake B08 is continuously increased. Simultaneously the pressure in multidisk brake B06 is reduced. The transition is smooth. Once the torque of 2nd gear is reached, the engine speed must be adapted to the 2nd gear level (super-elevation phase). For the speed adjustment, the pressure in the multidisk brake B08 is increased and - where required - the engine torque is reduced by the CDI control unit or ME-SFI [ME] control unit.

IMPORTANT A forced downshift occurs at excessively low RPM and a forced upshift occurs at an excessively high RPM. If the vehicle is stationary, 1st gear is automatically selected. It is possible to start off both in 1st or 2nd gear.

  Electrical function schematic for shift operation   PE27.19-P-2057-97FBC
  Overview of system components for automatic transmission (AT)   GF27.10-P-9992ANG 
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