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

Transmission 722.905 in model 166 as of model year 2016 

Transmission 722.905 in model 292 

Function requirements for Key-P, general 

Key-P, general 

The designation "Key-P" refers to the function by which the gear range "P" is engaged when the vehicle is stopped and the transmitter key (A8/1) is unplugged.

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

The intelligent servo module for DIRECT SELECT sends the status of the range selection position over the drive train CAN to the fully integrated transmission control unit, as well as over the drive train CAN, the ME-SFI [ME] control unit and the chassis CAN 1 to the electronic ignition lock control unit.

IMPORTANT The vehicle speed is calculated using the wheel speed signals.

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

Key-P function sequence 

The function sequence is subdivided into the following steps:

Function sequence for park pawl (except CODE 889 (KEYLESS-GO) or CODE 893 (KEYLESS-GO start function)) 

The park pawl only permits shifting out of selector lever position "P" using the DIRECT SELECT lever (S16/13) if the transmitter key is turned to the "circuit 15 ON" position, and the brake pedal is operated.

The "circuit 15 ON" signal is sent by the electronic ignition lock control unit to the chassis CAN 1 and read in by the ME-SFI [ME] control unit.

The ME-SFI [ME] control unit routes the signal over the drive train CAN to the fully integrated transmission control unit and to the intelligent servo module for DIRECT SELECT. The vehicle is secured mechanically by blocking the park pawl gear in the transmission.

The Electronic Stability Program control unit receives the status of the service brake and sends it over the chassis CAN 1, ME-SFI [ME] control unit and the drive train CAN to the fully integrated transmission control unit.

The intelligent servo module for DIRECT SELECT receives the command to engage the park pawl from the DIRECT SELECT lever over the steering column tube module control unit (N80), chassis CAN 1, ME-SFI [ME] control unit and the drive train CAN.

Function sequence for park pawl (with CODE 889 (KEYLESS-GO) or CODE 893 (KEYLESS-GO start function)) 

In vehicles with KEYLESS GO, the selector lever position "P" is engaged when the driver door is opened after the vehicle is parked. The left front door control unit (N69/1) routes the status of the left front door over the interior CAN (CAN B) to the KEYLESS-GO control unit (N69/5). The KEYLESS-GO control unit sends the status over the interior CAN and the chassis CAN 1 with the electronic ignition lock control unit interface to the ME-SFI [ME] control unit. This then forwards the request to engage gear range "P" over the drive train CAN to the intelligent servo module for DIRECT SELECT. The vehicle is secured mechanically by blocking the park pawl gear in the transmission.

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:

IMPORTANT The drive authorization system enable is sent by the electronic ignition lock control unit over chassis CAN 1, the ME-SFI [ME] control unit and the drive train CAN, and it is received by the fully integrated transmission control unit as well as the intelligent servo module for DIRECT SELECT.

  Electrical function schematic, Key-P   PE27.19-P-2058-97NBC
  Overview of system components for automatic transmission (AT)   GF27.10-P-9992ANN 

GF27.10-P-3029AHA Emergency-P function 

TRANSMISSION 722.9 in MODEL 166 up to model year 2016 

Function requirements for Emergency-P, general 

Emergency-P, general 

In emergencies, for example when undervoltage is detected in the on-board electrical system or communication to the intelligent servo module for DIRECT SELECT (A80) has a malfunction, the emergency motor (31) in the intelligent servo module for DIRECT SELECT is supplied with power via the electronic ignition lock control unit (N73) from the on-board electrical system battery, thereby triggering the Emergency-P function.

Emergency-P function sequence 

The function sequence is described in the following steps:

Function sequence for start position 

G14134838Courtesy of MERCEDES-BENZ USA

The on-board electrical system battery supplies the emergency motor (31) over the electronic ignition lock control unit in an emergency, e.g. when an undervoltage is detected in the on-board electrical system, whereupon the eccentric shaft (34) then rotates.

Function sequence for intermediate position 

G14134839Courtesy of MERCEDES-BENZ USA

The rotating eccentric shaft (34) presses on the release pin (32/4) of the left carriage half (32/1).

This in turn breaks the mechanical connection between the left carriage half (32/1) and the right carriage half (32/2).

Function sequence for end position 

G14134840Courtesy of MERCEDES-BENZ USA

The pre-compressed coil spring (32/3) pushes the two carriage halves apart. The right carriage half (32/2) slides along the threaded rod (33) to the right and pushes the range selector lever (35) to position "P". The eccentric shaft (34) rotates until the emergency motor (31) is no longer actuated. The actual position of the eccentric shaft (34) is detected by the eccentric shaft (40) position sensor and passed on to the electronics of the intelligent servo module for DIRECT SELECT.

Function sequence for cancellation 

The emergency P-function is automatically overridden, if the emergency case, which, e.g. is caused by undervoltage in the on-board electrical system, is no longer given. The main motor (30) rotates the threaded rod (33) over the drive belt (42). The left carriage half (32/1) runs on to the right carriage half (32/2), the coil spring (32/3) is pre-compressed again and the mechanical connection is restored.

IMPORTANT The Emergency-P function cannot be overridden manually.

  Overview of system components for automatic transmission (AT)   GF27.10-P-9992AHA 
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