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Transmission Control, Function - GF27.60-P-2002AND

Transmission 725.0 (except 725.017/066/096) in model 217, 222 

Function requirements for transmission control, general 

Transmission control, general 

The function of the fully integrated transmission control unit consists of the evaluation of various input signals (relevant for the transmission function). Depending on this, the electromechanical hydraulic valves (solenoids) are actuated, which in turn determine the transmission ratio of the transmission (gear selection) and the working pressure.

The solenoids are positioned on the fully integrated transmission control controller unit (Y3/8). This then realizes the hydraulic functionality.

The fully integrated transmission control unit actuates the following components electronically:

The following signals are processed by the fully integrated transmission control unit:

IMPORTANT The enable signal for the drive authorization system is issued by the electronic ignition lock control unit (N73) (transmitter key (A8/1) inserted) via the suspension FlexRay (Flex E), the powertrain control unit (N127) and the powertrain CAN (CAN C1) to the fully integrated transmission control unit.

Transmission control function sequence 

The function sequence is described in the following steps:

Function sequence for basic shift program 

The basic shift program includes upshift and downshift characteristics for all 9 gears, designed for:

Drive programs in vehicles up to model year 2018: 

The basic shifting program can be influenced by the driver using the transmission mode button (A40/9s8), which is located in the center console area. The button status is sent via the Audio/COMAND control panel (A40/9), the telematics CAN (CAN A), the COMAND controller unit (A40/3), the user interface CAN (CAN HMI), the electronic ignition lock control unit, the peripherals CAN (CAN PER), the powertrain control unit and the powertrain CAN to the fully integrated transmission control unit.

Drive programs in vehicles as of model year 2018 with code 448 (Touchpad): 

The basic shifting program can be influenced by the driver using the DYNAMIC SELECT switch (A40/9s19) which is located near the center console. The signal from the DYNAMIC SELECT switch (with code 448 (Touchpad)) is read in by the Audio/COMAND control panel (A40/9). The Audio/COMAND control panel sends the signal via the telematics CAN, the head unit (A26/17), the user interface CAN, the electronic ignition lock control unit and the suspension FlexRay to the Electronic Stability Program control unit (N30/4). The Electronic Stability Program control unit puts the information for the chosen transmission mode on the chassis FlexRay. The powertrain control unit receives this information and transmits it via the powertrain CAN to the fully integrated transmission control unit.

Drive programs in vehicles as of model year 2018 with code 446 (Touchpad only): 

The basic shifting program can be influenced by the driver using the DYNAMIC SELECT switch (N72s19) which is located near the center console. The signal from the DYNAMIC SELECT switch (with code 446 (Touchpad only)) is read in by the lower control panel (N72). The lower control panel sends the signal via the LCP LIN (LIN A3), the touchpad (A105), the telematics CAN, the head unit, the user interface CAN, the electronic ignition lock control unit and the suspension FlexRay to the Electronic stability Program control unit. The Electronic Stability Program control unit puts the information for the chosen transmission mode on the chassis FlexRay. The powertrain control unit receives this information and transmits it via the powertrain CAN to the fully integrated transmission control unit.

In vehicles up to model year 2018, the following drive programs are available: 

In vehicles as of model year 2018, the following drive programs are available: 

In vehicles with CODE 550 (trailer hitch), the trailer recognition control unit (N28/1) sends the trailer recognition status to the fully integrated transmission control unit via interior CAN (CAN B), electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN.

The shift programs are adapted by offsetting the characteristics, depending on:

The fully integrated transmission control unit monitors and shifts depending on:

The Electronic Stability Program control unit forwards the vehicle speed via the chassis FlexRay to the powertrain control unit. This passes on the signal to the fully integrated transmission control unit via the drive train CAN.

The driver can engage the desired gear ranges "P", "R", "N", "D" using the DIRECT SELECT lever. The status is sent via the steering column tube module control unit (N80), chassis FlexRay, powertrain control unit and drive train CAN to the fully integrated transmission control unit.

IMPORTANT The vehicle speed is calculated using the wheel speed signals.

IMPORTANTMessages and displays in instrument cluster (A1) 

Information about the selected gear (with the gear range) or the transmission mode is made available on the drive train CAN by the fully integrated transmission control unit. The powertrain control unit receives and forwards it via chassis FlexRay with the electronic ignition lock interface via the user interface CAN to the instrument cluster. This then actuates the relevant display via the following signals:

Gear indicator symbol 

Transmission mode display symbol 

Slow accelerator release:

Rapid accelerator release:

Function sequence for electronic and hydraulic transmission control 

While the electronic transmission control takes over the gear selection and adaptation of pressures to the torque to be transmitted, the power supply control of the transmission via the hydraulic elements of the fully integrated transmission controller unit. The oil supply for the hydraulic elements (hydrodynamic torque converter, shift elements, hydraulic transmission control) is provided via an oil pump (primary pump) connected to the drive shaft and/or via the electrical auxiliary oil pump. The transmission control system makes possible a precise adaptation of pressures to the respective operating states and to the engine output during the gearshift phase, resulting in a significant improvement in shift quality. It is possible to reach the engine rpm limit in the individual gears using full throttle and kickdown. The shift range can be changed while driving in the forward gears. The transmission control system prevents any impermissible high engine speeds with a downshift lockout device.

Furthermore, the transmission control offers the advantage of flexible adaptation to various vehicle versions.

IMPORTANT The electrical auxiliary oil pump ensures the oil supply of the hydraulic system when the combustion engine is switched off. It also supports the primary pump in the combustion engine's lower speed range. The CDI control unit (N3/9) (with diesel engine) or ME-SFI [ME] control unit (N3/10) (with gasoline engine) sends the "electric auxiliary oil pump ON" request to the fully integrated transmission control unit. The electrical auxiliary oil pump is actuated directly over the fully integrated transmission control unit. The fully integrated transmission control unit sends the status of the electrical auxiliary oil pump back to the CDI control unit or ME-SFI control unit.

Function sequence for kickdown 

The driver's wish for maximum acceleration is met by the kickdown function.

The kickdown function is activated from a pedal travel of > 90 %. The "Kick-down" signal is sent by the CDI control unit or ME-SFI control unit, which forwards the status of the engine management to the fully integrated transmission control unit via drive train CAN.

Based on this information the fully integrated transmission control unit actuates the solenoid valves so that upshifts and downshifts take place at an increased engine speed in order to achieve maximum performance.

The forced downshift into the next lower gear is performed when transmission temperatures are too high and vehicle speed is too low.

Function sequence for limp-home mode 

In case of a defect in one of the solenoids, the corresponding gear is blocked. This gear can no longer be selected.

The driver can engage the desired gear ranges "P", "R", "N" or "D" using the DIRECT SELECT lever.

The driver can choose been forward and reverse travel, engage the park pawl or, when in neutral, interrupt the power flow between torque converter and automatic transmission.

IMPORTANT The faults are stored in the fault memory. These can be read out using Xentry Diagnostics. The diagnostic connector (X11/4) receives the transmission control diagnosis status from the fully integrated transmission control unit via drive train CAN, powertrain control unit, chassis FlexRay, electronic ignition lock control unit and diagnostic CAN (CAN D).

IMPORTANTShort-term M program 

The short-term M mode is a temporary mode that is activated when the steering wheel gearshift buttons are operated. Pressing in the positive (+) direction triggers an upshift and pressing in the negative (-) direction triggers a downshift, insofar as this is permissible. If not, the current gear is maintained. After a specified time window, this function deactivates again automatically. The activated time can be extended by undershooting a minimum speed (e.g. by stopping), upon detection of a lateral acceleration or if the vehicle is in overrun mode. If none of the stated criteria are active anymore, the short-term M mode remains active for a specified period of time. After this remaining time has elapsed, a switch is made back to the initial shift program. In addition, the driver is shown a recommended shift operation in the instrument cluster. This is part of the gearshift recommendation that is also integrated. The driver can prematurely cancel the short-term M mode through specific actions, e.g. if he/she presses and holds the steering wheel upshift button in the "positive" direction (+), if the gear range changes or if he/she changes the transmission mode. If one of these preconditions is met, a switch is made back to the initial shift program.

  Electrical function schematic, fully integrated transmission control Transmission 725.0 (except 725.017/066/096) in model 217, 222 as of model year 2018 PE27.19-P-2061-97SEF
    Transmission 725.0 (except 725.017/066/096) in model 217, 222 up to model year 2018 PE27.19-P-2061-97SED
  Overview of system components for automatic transmission (AT)   GF27.10-P-9992AND 
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