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

Transmission 722.9 in model 463 as of model year 2013 

Function requirements for transmission control, general 

• Terminal 15 ON
• Self-diagnosis of the fully integrated transmission control unit (Y3/8n4) performed

The electronic ignition lock control unit (N73) sends the status of circuit 15 via chassis CAN 1 (E1), the CDI control unit (engine (N3/9) (engine 642) or ME-SFI control unit (N3/10) (engine 157, 273) or powertrain control unit (N127) (engine 176) and drivetrain CAN (CAN C) to the fully integrated transmission control unit.

Transmission control, general 

The function of the fully integrated transmission control unit consists of the evaluation of various input signals relevant to the transmission function. Based on this, the control solenoid valves are actuated which determine the transmission ratio of the automatic transmission (gear selection), the working pressure and the torque converter lockup.

The control solenoid valves are located in the hydraulic valve body assembly. This implements the hydraulic functions.

The fully integrated transmission control unit actuates the following control solenoid valves directly:

• Working pressure control solenoid valve (Y3/8y1)
• Clutch control solenoid valve K1 (Y3/8y2)
• Clutch control solenoid valve K2 (Y3/8y3)
• Clutch control solenoid valve K3 (Y3/8y4)
• Multidisk brake control solenoid valve B1 (Y3/8y5)
• Multidisk brake control solenoid valve B2 (Y3/8y6)
• Multidisk brake control solenoid valve B3 (Y3/8y7)
• Torque converter lockup clutch control solenoid valve (Y3/8y8)

The fully integrated transmission control unit reads in the signals from the following sensors directly:

• Turbine wheel RPM sensor (Y3/8n1)
• Rpm sensor for internal input speed (Y3/8n2)
• Output shaft RPM sensor (Y3/8n3)
• Selection range sensor (Y3/8s1)
• Transmission oil temperature sensor (Y3/8s2)

The transmission control function comprises the following subfunctions:

• Function sequence for basic shift program 
• Function sequence for electronic and hydraulic transmission control 
• Function sequence for kickdown 

Function sequence for basic shift program 

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

• Unladen vehicle
• Warm operating condition
• Smooth road
• Sea level

The basic shift program can be influenced by the driver by activating the "Low" off-road ratio, by activating the differential locks or by pressing the A/T transmission mode button (S16/12).

The A/T transmission mode button is located on the DIRECT SELECT INTERFACE (N150). The DIRECT SELECT INTERFACE reads in the status of the A/T transmission mode button directly and sends it via the drivetrain CAN to the fully integrated transmission control unit. The fully integrated transmission control unit performs the requested change and sends the request to display the transmission mode to the instrument cluster (A1) via the drivetrain CAN, CDI control unit (engine 642) or ME-SFI control unit (engine 157, 273) or powertrain control unit (engine 176), chassis CAN 1, electronic ignition lock control unit and chassis CAN 2 (CAN E2). The instrument cluster then actuates the transmission mode display (A1p16).

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

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

Slow accelerator release: Undesired downshifts in the upper vehicle speed range are prevented.

Fast accelerator release: Upshifting to the next gear is prevented and only permitted again when the vehicle accelerates slowly.

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

• Vehicle speed
• Drive position
• Accelerator pedal position
• Transmission mode selection
• Selected gear, with manual transmission mode "M" (except code ZU8 (USA national version) and as of model year 2015 except code 990 (AMG vehicle documents/identification plate control))

The instrument cluster sends the vehicle speed via chassis CAN 2, the electronic ignition lock control unit, CDI control unit (engine 642) or ME-SFI control unit (engine 157, 273) or powertrain control unit (engine 176) and drivetrain CAN to the fully integrated transmission control unit.

The DIRECT SELECT INTERFACE sends the selected gear range and the status of the A/T transmission mode button via the drivetrain CAN to the fully integrated transmission control unit.

The CDI control unit (diesel engine) or the ME-SFI control unit (gasoline engine) detects the accelerator pedal position and sends this information via the drivetrain CAN to the fully integrated transmission control unit.

Function sequence for electronic and hydraulic transmission control 

While the electronic transmission control is responsible for gear selection and adaptation of pressures to the torque to be transmitted, power supply control for the automatic transmission is performed by the hydraulic elements of the fully integrated transmission control controller unit. The oil supply for the hydraulic elements such as hydrodynamic torque converter, shift elements and hydraulic transmission control is provided through an oil pump (primary pump) connected to the torque converter or through the electric transmission oil pump (M42) (with code MJ7 (ECO start/stop function)). 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 any impermissible 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.

Transmission 722.9 in model 463 as of model year 2013 with code MJ7 (ECO start/stop function)

The electric transmission 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 internal combustion engine's lower speed range. The fully integrated transmission control unit sends the request to switch on the electric transmission oil pump via the drivetrain CAN to the transmission oil auxiliary pump control unit (N89). The transmission oil auxiliary pump control unit actuates the electric transmission oil pump directly.

Function sequence for kickdown 

Maximum acceleration of the vehicle is achieved by means of the kickdown function. The kickdown is activated as of an accelerator pedal travel > 90 %.

The accelerator pedal position is detected by the CDI control unit (diesel engine) or by the ME-SFI control unit (gasoline engine) and is sent via the drivetrain 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.

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

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