Crankcase Ventilation System, Function - GF01.20-P-0001MRH

Engine 274.9 in model 205.047/053/054/147/247/253 

Engine 274.9 in model 253.354/954 

Function requirements for crankcase ventilation system, general 

• Circuit 87M (Engine management ON)

  Crankcase ventilation system, general 

  The crankcase ventilation system ensures under all operating conditions of the engine that overpressure and excess gases are dissipated from the crankcase and fed back to the engine via the intake air system for combustion. To balance out the pressure ratio, a separate line is attached for engine ventilation.

  The control of the crankcase ventilation system is dependent on the following sensors and signals:

• Pressure sensor downstream of throttle valve (B28/7), engine load
• Accelerator pedal sensor (B37), accelerator pedal position
• Front SAM control unit (N10/6), outside temperature via interior CAN (CAN B) to electronic ignition lock control unit (N73), via chassis FlexRay (Flex E) to powertrain control unit (N127) and via drive train CAN (CAN C1) to ME-SFI [ME] control unit (N3/10)

  Crankcase ventilation system function sequence 

  The function sequence of the crankcase ventilation system is described in the following points:

• Function sequence for crankcase ventilation system partial load operation 
• Function sequence for crankcase ventilation system wide open throttle operation 

  Function sequence for crankcase ventilation system partial load operation 

In partial-load range, ventilation is performed starting from the oil separator to the charge air distributor. To do so, the partial load operation crankcase ventilation system valve (Y58/2) is arranged in the partial-load vent line.

The valve is actuated in deceleration mode by the ME-SFI [ME] control unit and closes the partial-load vent line from the crankcase to the charge air distributor.

The inflow of exhaust from the crankcase during the mixture adaptation and disruptive background noise are thus avoided. If there is no actuation by the ME-SFI [ME] control unit, the valve is permanently open.

Function sequence for crankcase ventilation system wide open throttle operation 

In wide open throttle operation, ventilation is performed starting from the oil separator to the air intake pipe.

The wide open throttle operation vent line heater element (R39/2) is located in the full load vent line and prevents the freezing of the ventilation system. To do this, the heating element is actuated by the ME-SFI [ME] control unit as soon as outside temperatures of under 7°C are measured.

Freezing of the crankcase ventilation system and associated engine damage are thus prevented.

View of engine from left, except model 205.047/053/054/147/247/253 

Courtesy of MERCEDES-BENZ USA