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

TRANSMISSION 722.9 in MODEL 166 up to model year 2016 

Function requirements for transmission control, general 

• Circuit 87 (connected circuit 15) ON
• Function test of fully integrated transmission control unit (Y3/8n4) carried out

Transmission control, general 

The transmission control system electronically actuates the control solenoid valves. The valves are located in the hydraulic valve body assembly. This realizes the hydraulic functionality and is part of the fully integrated transmission control controller unit (Y3/8). The function of the fully integrated transmission control unit basically consists of the evaluation of various input signals relevant to the transmission function. Based on this, eight electromechanical control solenoid valves are actuated that then determine the transmission ratio (gear selection), the working pressure and the torque converter lockup.

Transmission control function sequence  The function sequence is described in the following steps:

• Function sequence for basic shift program 
• Function sequence for electronic and hydraulic transmission control 
• Function sequence for kickdown 
• Function sequence for limp-home mode 

Function sequence for basic shift program 

The basic shift program includes upshift and downshift characteristics for all 7 gears, designed for:

• Empty vehicle
• Operating temperature
• Smooth road
• Sea level

The driver can influence the following:

• The offroad program button (N72s38) (with engine 157/276/278/642 and engine 651 with CODE 498 (Japan version)), except CODE 430 (On & Offroad package)
• The A/T transmission mode button (N72s32) (with engine 651 except CODE 498 (Japan version) and except CODE 430 (On & Offroad package)
• The offroad package transmission mode controller (N72/3s1) (with CODE 430 (On & Offroad package))

Using the basic shifting mode.

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

• Load condition of vehicle
• Change in driving resistance
• Accelerator pedal movement

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

• Vehicle speed
• Gear selector switch position
• Accelerator pedal position
• Transmission mode selection
• Engaged gear, with Manual "M" transmission mode with CODE 430 (On & Offroad package)
• Signals on the drive train CAN (CAN C)

TRANSMISSION 722.9 in MODEL 166 up to model year 2016

with CODE 430 (On & off-road package)

Transmission mode "M" is only available with CODE 430 (On & Offroad package). Vehicles without On & Offroad package do not have transmission mode "M". On these vehicles, transmission mode "M" is replaced by the "Short-term M mode".

Slow accelerator release:

• Undesired downshifts in the upper vehicle speed range are prevented

Rapid accelerator release:

• Upshifting to the next gear is prevented and only permitted again when the vehicle accelerates slowly

Function sequence for electronic and hydraulic transmission control 

While the electronic transmission control system is responsible for gear selection and adaptation of pressures to the torque to be transmitted, power supply control for the transmission is performed by the hydraulic elements of the fully integrated transmission controller unit. The oil supply for the hydraulic elements, such as hydrodynamic torque converter, shift elements and hydraulic transmission control, is provided by an oil pump connected to the torque converter or through the electric transmission oil pump (M42). 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 transmission control system prevents impermissibly high engine speeds with a downshift lockout device. Furthermore, the transmission control system offers the advantage of a flexible adaptation to various vehicle and engine versions.

The electrical auxiliary pump supplies the oil to the hydraulic system when the internal combustion engine is switched off. It also supports the primary pump during coast down shifting in hot idling. This is actuated through the gear oil auxiliary pump control unit (N89).

Function sequence for kickdown 

The driver's wish for maximum acceleration is met by the kickdown function. The kickdown function is activated as of a pedal travel > 90%. The "Kick-down" signal is received by the CDI control unit (N3/9) (for diesel engines) or the ME-SFI [ME] control unit (N3/10) (for gasoline engines) and sent over the drive train CAN to the fully integrated transmission control unit. Based on this information the fully integrated transmission control unit actuates the control solenoid valves so that upshifts and downshifts take place at an increased engine speed in order to achieve maximum performance.

Function sequence for limp-home mode 

If the signals are implausible, the transmission control system is only partially operational and switches to the programmed emergency performance map. Using the DIRECT SELECT lever (S16/13), the driver can engage the desired gear ranges "P", "R", "N", "D". 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 transmission.

TRANSMISSION 722.9 in MODEL 166 as of model year 2013 up to model year 2016

Introduction of short-term M program 

The gear limitation is replaced by the function "Short-term M mode". 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 induces an upshift, pressing in the negative (-) direction induces 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 a deceleration phase. If none of the stated criteria are active anymore, the short-term M mode remains active for a prescribed remaining time. After this remaining time expires, the initial shift mode is returned to. The driver is also shown a recommended shift operation in the instrument cluster (A1). 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 (S111/1) 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.

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