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

TRANSMISSION 724.2 in MODEL 212 

Sectional view of electrohydraulic park pawl actuation 

Fig 1: Sectional View Of Electrohydraulic Park Pawl Actuation (1 Of 2)

Courtesy of MERCEDES-BENZ USA

Fig 2: Sectional View Of Electrohydraulic Park Pawl Actuation (2 Of 2)

Courtesy of MERCEDES-BENZ USA

Function requirements for Emergency-P, general 

• Circuit 87 (connected circuit 15) ON

Emergency-P, general 

During malfunctions, if, for example, undervoltage prevails in the on-board electrical system or communication with the fully integrated transmission control unit (Y3/8n4) is interrupted, the park pawl lift solenoid in the fully integrated transmission controller unit (Y3/8) is supplied with power from the additional battery (G1/7) through the electronic ignition lock control unit (N73) and triggers the Emergency-P function.

When the Emergency-P function is active, the piston rod lock (10) is released by the notched lever (9), the park pawl switchover valve (Y3/8y11) is then in deenergized state and pressure is not applied to the hydraulic cylinder. The pretension spring (6) is supported on the piston rod guide (41) of the piston housing (5) and it moves the piston rod (10) into shift position "P".

Park pawl lift solenoid

The park pawl lift solenoid is pulse actuated to minimize the power loss in the fully integrated transmission control unit. The solenoid is actuated by the fully integrated transmission control unit or electronic ignition lock control unit, if the on-board electrical system voltage is interrupted.

The time period over which the fully integrated transmission control unit energizes the park pawl lift solenoid, is generally measured such that the piston rod (10) reaches the new position before it is de-energized again.