Emergency Default Mode, Function - GF27.60-P-3012KJ

TRANSMISSION 700.4 in MODEL 453.0/3/4 

Function requirements for limp-home mode, general 

• Circuit 15 ON

Limp-home mode, general 

On the dual clutch transmission the limp-home mode function can be divided into the following partial functions:

• Sub-transmission limp-home mode, even/odd gears 
• Transmission limp-home mode, power-free state 

The dual clutch transmission control unit (N15/13) monitors the status of the transmission control by means of the following sensors:

• Transmission mode recognition sensor (B56/1)
• Rpm sensor 1, transmission input shaft with direction detection (B108)
• Rpm sensor 2 transmission input shaft (B109)
• Brake lights switch (S9/1)
• Steering wheel downshift button (S110/1) over steering wheel clock spring contact (A45/1)
• Steering wheel upshift button (S111/1) over steering wheel clock spring contact
• Accelerator pedal position from accelerator pedal sensor (B37) over ME-SFI [ME] control unit (N3/10) and drive train CAN (CAN C)
• Wheel speeds, from left front axle rpm sensor (L6/1), right front axle rpm sensor (L6/2), left rear axle rpm sensor (L6/3), right rear axle rpm sensor (L6/4) over the Electronic Stability Program control unit (N30/4), interior CAN (CAN B), drive train CAN with the ME-SFI [ME] control unit interface

The dual clutch transmission control unit checks the plausibility of the sensor values based on the characteristics maps stored in the control unit.

The dual clutch transmission control unit also monitors the function of the following actuators:

• Clutch actuator 1 (M14)
• Clutch actuator 2 (M15)

Sub-transmission limp-home mode, even/odd gears 

If one of the sub-transmissions fails, the following gears are no longer available:

• Sub-transmission 1: Gears "1", "3", "5" as well as the reverse gear "R" because the 1st gear must also be engaged to permit power flow transfer in reverse gear
• Sub-transmission 2: Gears "R", 2, 4, 6"

If a clutch actuator malfunctions in the clutch control system or if a shift motor for the intermediate gears comes to a standstill, one of the sub-transmissions will also no longer be available, depending on the motor which is defective or cannot be actuated.

Transmission limp-home mode, power-free state 

The complete frictional connection has failed.

Use the following procedure to check whether this involves a sporadic error:

• Switch off ignition (instrument cluster (A1) must be off).

If the message does not appear again, the error status in the dual clutch transmission control unit has been changed from "ACTIVE" to "STORED" and continued driving is possible without restrictions. If the error persists, continued driving is no longer possible and the nearest Mercedes-Benz workshop must be contacted.

Fault diagnosis

The transmission status is sent by the dual clutch transmission control unit over the drive train CAN, ME-SFI [ME] control unit, interior CAN to the diagnostic connector (X11/4). From there the dual clutch transmission can then be read out and analyzed through XENTRY Diagnostics.

	Electrical function schematic for limp-home function		PE27.19-P-2065-97BBA
	Overview of system components for dual clutch transmission		GF27.10-P-9994KJ