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

Transmission 724.2 in model 205, 253 

Function requirements, general 

• Terminal 15 ON
• Internal combustion engine ON

The electronic ignition lock control unit (N73) transmits the status of circuit 15 via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the fully integrated transmission control unit (Y3/8n4).

Emergency running 

In the event of critical faults, the fully integrated transmission control unit switches to limp-home mode. This avoids damage to the automatic transmission and ensures that a safe driving condition is maintained. The fully integrated transmission control unit stores information about the fault that has occurred together with the assigned fault code in the fault memory. The fully integrated transmission control unit then sends the limp-home mode active message over the drive CAN to the CDI control unit (N3/9) (diesel engine) or the ME-SFI [ME] control unit (N3/10) (gasoline engine). The CDI control unit or the ME-SFI [ME] control unit then sends the engine diagnosis indicator lamp switch-on request (A1e58) over the engine CAN (CAN C), powertrain control unit (N127), chassis FlexRay (Flex E), electronic ignition lock control unit (N73) and the user interface CAN to the instrument cluster (A1). The instrument cluster then actuates the engine diagnosis indicator lamp.

The fully integrated transmission control unit locks the gear concerned if necessary. The vehicle can therefore be safely driven to the nearest Mercedes-Benz service operation.

If the fully integrated transmission control unit fails (e.g. open circuit, no power supply) limp-home mode cannot be activated. In this case the park pawl is activated. The park pawl can only be released hydraulically via the park pawl switchover valve (Y3/8y11).

The fully integrated transmission control unit can save up to 16 faults.

In the event of a hydraulic fault, the "Charge while stationary" function is deactivated. The electrical ancillaries are only operated de-rated.