Emergency-P Function - GF27.10-P-3029ANR

Transmission 725.0 (except 725.096) in model 257, 290 

up to model year 2021 

Sectional view of electrohydraulic park pawl actuation 

Courtesy of MERCEDES-BENZ USA

Function requirements for Emergency-P, general 

• Circuit 15 ON

Emergency-P, general 

A fault in the park pawl lift solenoid, which leads to the notched lever (11d) of the parking lock actuator in position "Emergency-P" no longer being able to be unlocked by the solenoid, may be compensated for by the notched lever release pin (11g) hydraulically opening the notched lever (11d). The required hydraulic pressure here is provided by the electric auxiliary oil pump (M42) when the internal combustion engine is stopped.

When the Emergency-P function is active the locking device for the piston rod (11f) is canceled by the notch lever (11d). If the hydraulic pressure level is too low, the notch lever release pin (11g) prevents the park pawl lift solenoid having pressure applied to it towards "Emergency-P". If the hydraulic pressure level is too low, the lubrication pressure solenoid (Y3/8y12) is energized via the park pawl lift solenoid. This in turn prevents the hydraulic cylinder from having pressure applied to it in the "Emergency-P" direction. The compression spring (11l) is supported on the piston rod guide of the piston housing (11) and thus displaces the piston rod (11f) into the shift position"P".

Park pawl lift solenoid

The park pawl lift solenoid is actuated in pulses to minimize noise in the vehicle. Normally, the solenoid is actuated by the control unit for the fully integrated transmission control electric controller unit (Y3/8n4) or by the electronic ignition lock control unit (N73) when the on-board electrical system voltage is interrupted.