Transmission control, function - GF27.60-P-2002AHW

WARNING: This page is about a different car, the 2011 Mercedes-Benz C300, 2010 Mercedes-Benz C300, 2009 Mercedes-Benz C300, and 2008 Mercedes-Benz C300. However, it is still accessible from the selected car via links, so may be relevant.

TRANSMISSION 722.9 (except 722.930) in MODEL 204.0 as of model year 2009/YoM 08

Function requirements for transmission control, general

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

Transmission control, general

The fully integrated transmission control (VGS) controls all functions of the transmission.

The function of the fully integrated transmission control unit basically consists of the evaluation of various input signals relevant for the transmission function and actuation of the following actuators which for their part determine the transmission gear ratio (gear selection), the working pressure and torque converter lockup:

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)

Transmission control function sequence

The function sequence is described in the following steps:

Function sequence for basic shift program
Function sequence for fully integrated transmission control (VGS)
Function sequence for kickdown
Function sequence for limp-home mode

Implementation dates and validities for code (B03) ECO start/stop function

Model 204.0/2 as of model year 2012/YoM 11 model refinement package with engine 271.8, 276.9, 651.9
Model 204.025/225 as of 1.6.2011 with engine 642.8
Model 204.3
Model 204.9 as of 1.6.2011 with engine 651.9
Model 204.988 as of 1.1.2011 with engine 276.9

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 basic shift program can be influenced by the driver through the automatic transmission's transmission mode button (S16/12). 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
Selector lever position
Accelerator pedal position
Transmission mode selection
Selected gear, in transmission mode Manual "M" (model 204.077/277, model 204.0/2, model 204.3 except code (494) USA version or model 204.9 with code (430) Off-road package and code (952) Sport package)
Signals on the drive train CAN (CAN C)

Slow accelerator release:

Undesired downshifts in the upper vehicle speed range are prevented

Rapid accelerator release:

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

Function sequence for fully integrated transmission control (VGS)

Whereas the electronic transmission control is responsible for gear selection and adaptation of pressures to the torque to be transmitted, the transmission's power supply control is effected through the hydraulic elements of the fully integrated transmission controller unit (Y3/8). The oil supply for the hydraulic elements such as hydrodynamic torque converter, actuators 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 (B03) 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 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.

For code (B03) ECO start/stop function

The electric transmission oil pump provides the hydraulic system's oil supply when the internal combustion engine is switched off. It also supports the primary pump when the combustion engine is operating in the low speed range. 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 lead from the CDI control unit (N3/9) or ME-SFI [ME] control unit (N3/10) to the fully integrated transmission control unit through the drive CAN 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

In the case of implausible signals the fully integrated transmission control (VGS) is still only operational to a limited extent and shifts into the programmed limp-home mode performance map. The fault is stored in the fault memory with the assigned fault code and the engine diagnosis indicator lamp (A1e58) in the instrument cluster (A1) is actuated.

The driver can engage the required gear ranges "P", "R", "N", "D" using the selector 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 transmission.