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

Transmission 725.0 (except 725.096) in model 257, 290 

up to model year 2021 

Function requirements for shift operation, general 

• Circuit 15 ON
• Combustion engine running
• Engine speed from CDI control unit (N3/9) (with diesel engines) or ME-SFI [ME] control unit (N3/10) (with gasoline engines)
• Vehicle speed signal
• Automatic transmission not in limp-home mode
• Complete and fault free signal transmission over drive train CAN (CAN C1)

Shift operation, general 

To check the function requirements, the control unit for the electric controller unit of the fully integrated transmission control (Y3/8n4) reads in the following signals over the drive CAN:

• Circuit 15 ON from electronic ignition lock control unit (N73) via suspension FlexRay (Flex E), powertrain control unit (N127)
• Running combustion engine from CDI control unit or from ME-SFI control unit
• Engine speed from CDI control unit or from ME-SFI control unit
• Vehicle speed from instrument cluster (A1) over the user interface CAN (CAN HMI), electronic ignition lock control unit, chassis FlexRay and the powertrain control unit

The CDI control unit or the ME-SFI [ME] control unit sends the engine management status over the drive CAN to the control unit for the electric controller unit of the fully integrated transmission control.

The Electronic Stability Program control unit (N30/4) sends the signal for the operational drivetrain over the suspension FlexRay, powertrain control unit and the drive CAN to the control unit for the electric controller unit of the fully integrated transmission control.

The electric controller unit of the fully integrated transmission control (Y3/8) converts the electrical signals sent by the control unit for the electric controller unit of the fully integrated transmission control into hydraulic signals.

Drive ranges "R", "N", "D1" to "D9" and "P" can be engaged by operating the DIRECT SELECT lever (S16/13).

The DIRECT SELECT lever sends the information on the selected drive range "P", "R", "N", "D1" to "D9" via the steering column tube module control unit (N80), which then places the signal on the suspension FlexRay. Once here the signal is recorded by the powertrain control unit and sent over the drive CAN to the control unit for the electric controller unit of the fully integrated transmission control.

The corresponding gear range is then engaged.

The shift range for engaged gear range "D1" to "D9" is shown on the instrument cluster.

Although the shift range can be changed in the forward gears while driving, the control unit for the electric controller unit of the fully integrated transmission control unit prevents a shift operation if the engine speeds are too high or too low.

Messages and displays in instrument cluster 

Information about the selected gear, drive range or the drive program are sent by the control unit for the electric controller unit of the fully integrated transmission control to the drive CAN. The powertrain control unit receives and forwards it via the suspension FlexRay, electronic ignition lock, user interface CAN to the instrument cluster.

This then actuates the relevant display via the following signals:

Instrument cluster 

• Gear indicator, actuation
• Transmission mode display, actuation

The following component parts are actuated by the control unit for the electric controller unit of the fully integrated transmission control:

• Park pawl lift solenoid (Y3/8l1)
• Lubrication pressure solenoid (Y3/8y12)
• K81 clutch control solenoid (Y3/8y13)
• K38 clutch control solenoid (Y3/8y14)
• K27 clutch control solenoid (Y3/8y15)
• B08 multidisk brake control solenoid (Y3/8y16)
• B05 multidisk brake control solenoid (Y3/8y17)
• B06 multidisk brake control solenoid (Y3/8y18)
• Working pressure solenoid (Y3/8y19)
• Torque converter lockup clutch solenoid (Y3/8y20)

The following signals are processed by the control unit for the electric controller unit of the fully integrated transmission control:

• Pressure sensor (Y3/8b5)
• Turbine wheel RPM sensor (Y3/8n1)
• Input speed RPM sensor (Y3/8n2)
• Output shaft RPM sensor (Y3/8n3)
• Transmission oil temperature sensor (Y3/8s2)
• Park pawl position sensor (Y3/8s4)

Function sequence for shift operation 

The function sequence is described in the following steps:

• Function sequence for shifting up and down 
• Function sequence for 1 to 2 shift 

Function sequence for shifting up and down 

The basic shifting program can be influenced by the driver through the DYNAMIC SELECT switch (N72/4s1), which is located in the area of the center console in the left lower control panel (N72/4).

Except model 257.361 

The left lower control panel sends the signal over the LCP-LIN (LIN A3), the Audio/COMAND control panel (A40/9), the telematics CAN (CAN A), 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. 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 sends it over the drive CAN to the control unit for the electric controller unit of the fully integrated transmission control.

Model 257.361 

The left lower control panel sends the signal via the LCP-LIN, Audio/COMAND control panel, telematics CAN, head unit, user interface CAN, electronic ignition lock control unit and suspension FlexRay to the Drive Unit control unit (N145/1). The Drive Unit control unit puts the information for the selected drive program on the suspension FlexRay. The powertrain control unit receives this information and sends it over the drive CAN to the control unit for the electric controller unit of the fully integrated transmission control.

The following transmission modes are available:

• Comfort
• Economy
• Sport
• Sport+
• Individual

Transmission 725.0 in model 257.361

up to model year 2021

The manual shift mode button (N72/4s12) can be used to select the "manual shift mode".

By pressing the steering wheel downshift button (S110/1) or the steering wheel upshift button (S111/1) in the transmission modes, the driver can select the following functions:

• The short-term M mode is activated by pressing the steering wheel gearshift buttons in the transmission modes. This allows the driver to change gear using the steering wheel gearshift buttons without having to select the short-term M mode beforehand. The previous gear limitation/shift into optimum gear function using the steering wheel gearshift buttons has been discontinued.
• The short-term M mode is automatically deactivated again after a specific period. This time interval starts again after every additional press of a button. The activity of the function is extended depending on the wide open throttle and lateral acceleration involved.
• In transmission mode "E", in comparison to the transmission modes "S" and "S+", a shorter shift range (shifting at low engine speed) and therefore a lower drive torque is available when starting off forwards and starting off in reverse. This allows for more economical and comfortable driving because the gears are not driven to the limit.

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

The status of the steering wheel downshift button and the steering wheel upshift button is read in by the control unit for the electric controller unit of the fully integrated transmission control over the steering wheel electronics (N135), steering LIN (LIN E1), steering column tube module control unit, suspension FlexRay, powertrain control unit and the drive CAN.

Function sequence for 1 to 2 shift 

The B05 multidisk brake, the B06 multidisk brake and the K38 multiplate clutch are engaged in 1st gear. When shifting from 1stgear to 2nd gear, the B05 multidisk brake is disengaged and the K81 multiplate clutch is engaged.

The shift operation is started by the control unit for the electric controller unit of the fully integrated transmission control. The K81 multiplate clutch is filled and the pressure in the K81 multiplate clutch is continuously increased. At the same time, the pressure in the multidisk brake B06 is reduced.

This involves a flowing transition. When the 2nd gear torque is reached, the engine speed must be adapted to the 2nd gear level (elevation phase).

This speed adjustment is achieved by increasing the pressure in the K81 multiplate clutch and, if necessary, by the CDI control unit or ME-SFI [ME] control unit reducing engine torque.

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.

Short-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. stopping), upon recognition of a lateral acceleration or if the vehicle is in deceleration 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.

Shifts, which could result in non-permissible high or low engine speeds, are not performed.