Key-P Function - GF27.10-S-3028TRF

Model 447, 448 with transmission 725 

with code XM0 (Facelift) 

except code XM7 (MOPF II) 

Key-P function requirements, general 

• Circuit 15ON
• 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 fully integrated transmission control (VGS) electric controller unit (N1515) reads in the following signals to check the function requirements:

• Status of "Circuit 15 ON" from electronic ignition lock (EZS) control unit (N73)
• Status of service brake from Electronic Stability Program (ESP) control unit (N30/4)
• Vehicle speed signal from instrument cluster (IC) control unit (A1/1)

The vehicle speed is calculated using the wheel speed signals.

Function sequence for Key-P 

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 park pawl is engaged and disengaged purely by electrohydraulic means, either by operating the DIRECT SELECT selector lever (S16/13) or depending on various factors such as:

• Opening driver's door while drivetrain is operational
• Disconnecting ignition key

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 approval from drive authorization system stage 4 (FBS 4)
• Brake pedal not actuated
• "Circuit 15ON" not active

The drive authorization system enable signal is issued by the electronic ignition lock control unit (EZS).

	Emergency-P function		GF27.10-S-3029TRF
	Overview of system components of automatic transmission (AT)		GF27.10-S-9992TRF