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

Transmission 725.0 in model 253 

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.

To check the function requirements, the fully integrated transmission control unit (Y3/8n4) reads in the following signals:

• "Circuit 15 ON" status from electronic ignition lock control unit (N73) (transmitter key (A8/1) inserted) over the chassis FlexRay (Flex E), powertrain control unit (N127) and the drive train CAN (CAN C1)
• Service brake status from Electronic Stability Program control unit (N30/4) via chassis FlexRay, powertrain control unit and drive train CAN
• Vehicle speed signal from instrument cluster (A1) via user interface CAN (CAN HMI), electronic ignition lock control unit, chassis

  FlexRay, powertrain control unit and powertrain CAN

The vehicle speed is calculated using the wheel speed signals.

If the transmitter key is turned to position "0" (circuit 15 C) and removed while the vehicle is driving or rolling, the automatic transmission is automatically shifted to gear range "N". As a result, the vehicle can roll "freely".

Key-P function sequence 

The function sequence is described in the following steps:

• Function sequence for park pawl (except CODE 889 (KEYLESS-GO)) 
• Function sequence for park pawl (with CODE 889 (KEYLESS-GO)) 
• Function sequence for selector lever position "P" lock 
• Function sequence of Emergency-P (see document Emergency-P, function) 

Function sequence for park pawl (except CODE 889 (KEYLESS-GO)) 

The park pawl only permits shifting out of position "P" if the transmitter key is turned to position "circuit 15 ON" and the brake pedal is depressed. The fully integrated transmission control unit receives the signal to engage the park pawl from the DIRECT SELECT lever via the steering column tube module control unit (N80), chassis FlexRay, powertrain control unit and drive train CAN.

The vehicle is secured mechanically by blocking the park pawl gear in the automatic transmission.

Function sequence for park pawl (with CODE 889 (KEYLESS-GO)) 

On vehicles with CODE 889 (Keyless Go), a shift is made to gear range "P" when the driver door is opened by the driver after parking the vehicle. The left front door control unit (N69/1) transmits the status of the left front door via interior CAN (CAN B), electronic ignition lock control unit, chassis FlexRay, powertrain control unit and drive train CAN to the fully integrated transmission control unit.

Function sequence for selector lever position "P" lock 

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

• No enable signal for the drive authorization system stage 4 (FBS4)
• Brake pedal not actuated
• Transmitter key not in position "Circuit 15 ON"

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.