Overview
This document contains information on:
Function requirements
Function
Function requirements
Engine management ON (circuit 87M)
Engine in operation
Function
Sub-transmission limp-home mode, even/odd gears
In the even of a fault in or failure of the even/odd gears actuator, one of the sub-transmissions will no longer be available, depending on the actuator which is defective or cannot be actuated. In the event of failure of sub-transmission 1, the gears 1-3-5-7 are no longer available. In the event of failure of sub-transmission 2, the gears 2-4-6-R are no longer available.
Transmission limp-home mode, power-free state
If there is a fault in the actuation of both clutches, e.g. due to failure of the clutch 1/2 actuator pump, there is no power flow. The vehicle is no longer propelled.
Transmission limp-home mode, transmission overtemperature
While driving, friction at the clutch plates and gear sets produces high transmission oil temperatures. Particularly high waste heat is produced in the area of the clutches. The waste heat is absorbed by the transmission oil and dissipated into the environment via the transmission oil cooling circuit. The transmission oil temperature can exceed a predefined threshold value, e.g. due to multiple start-off procedures on uphill gradients and at high outside temperatures. The combustion engine control unit reduces the engine output until the transmission oil temperature is back below the threshold value. If the transmission cooling system fails, e.g. due to failure of the dual clutch oil cooling pump, it is possible to continue driving up to a defined threshold value.
Transmission limp-home mode, park pawl system
The park pawl prevents the vehicle from moving off by itself when the selector lever is in position "P" in normal operation. The park pawl cannot be engaged if the actuation of the following components is faulty or incorrect:
Park pawl lift solenoid
Selector drum
Even/odd gears actuator
The vehicle cannot be secured against rolling away via the selector lever position "P". Alternatively, it is possible to prevent it from rolling by actuating the electric parking brake.