Key-P Function - GF27.10-P-3028ANR

Transmission 725.0 (except 725.096) in model 257, 290 

up to model year 2021 

Key-P function requirements, general 

• Circuit 15 ON
• Brake pedal operated
• Vehicle speed < 8 km/h

Key-P, general 

The designation "Key-P" comprises all the functions, which in addition to the parking brake, help to secure the vehicle to prevent it from rolling away unintentionally.

The control unit for the fully integrated transmission control electric controller unit (Y3/8n4) reads in the following signals to check the function requirements:

• "Circuit 15 ON" status from electronic ignition lock control unit (N73) via suspension FlexRay (Flex E), powertrain control unit (N127) and drive CAN (CAN C1)
• Service brake status from Electronic Stability Program control unit (N30/4) via suspension FlexRay, powertrain control unit and drive CAN
• Vehicle speed signal from instrument cluster (A1) via user interface CAN (CAN HMI), electronic ignition lock control unit, suspension FlexRay, powertrain control unit and drive CAN

The vehicle speed is calculated using the wheel speed signals.

Key-P function sequence 

The function sequence is described in the following steps:

• Park pawl function sequence 
• Function sequence for selector lever position "P" lock 
• Function sequence of Emergency-P (see document Emergency-P, function) 

Park pawl function sequence 

The automatic transmission is shifted to drive range "P" when the driver opens the driver door after switching off the engine. The left front door control unit (N69/1) sends the status of the left front door over the interior CAN (CAN B), electronic ignition lock control unit, suspension FlexRay, powertrain control unit and the drive CAN to the control unit for the fully integrated transmission control electric controller unit. The vehicle is secured mechanically by blocking the park pawl gear in the automatic transmission.

Function sequence for selector lever position "P" lock 

A gear range change from position "P" cannot be executed if the following conditions are fulfilled:

• No enable signal from drive authorization system level 4 (FBS4)
• Brake pedal not actuated
• "Circuit 15 ON" not active

The enable signal from the drive authorization system is sent from the electronic ignition lock control unit via chassis FlexRay, powertrain control unit and drive train CAN.

	Electrical function schematic, Key-P		PE27.19-P-2058-97XBA
	Emergency-P function		GF27.10-P-3029ANR
	Overview of system components of automatic transmission (AT)		GF27.10-P-9992ANR