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Home >> Mercedes Benz >> 2021 >> E350 Base >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Mixture Formation - 213 Chassis 1 Of 5 >> Basic Knowledge >> Engine Limp-Home Mode, Function >> Engine Limp-Home Mode, Function - GF07.10-P-1019MNA

Engine Limp-Home Mode, Function - GF07.10-P-1019MNA

Engine 177.9 in model 205, 253 

Engine 177.9 in model 213 

up to model year 2021 

Function requirements, general 

IMPORTANT The ME-SFI [ME] control unit (N3/10) detects the engine running by evaluating the signals of the crankshaft Hall sensor (B70). The ME-SFI [ME] control unit directly reads in the signals of the crankshaft Hall sensor.

Engine limp-home mode, general 

The task of the engine limp-home mode consists of ensuring continued safe driving in the case of malfunctions on individual components of the engine management.

The ME-SFI [ME] control unit controls the engine limp-home mode based on signals from the following components:

The ME-SFI [ME] control unit also evaluates the status of the service brake. The Electronic Stability Program control unit (N30/4) transmits this via the chassis FlexRay (Flex E), the powertrain control unit (N127) and the drive train CAN (CAN C1) to the ME-SFI [ME] control unit.

Depending on the fault, a distinction can be made between the following engine limp-home mode variants:

Limp-home mode upon failure of accelerator pedal sensor 

The accelerator pedal sensor detects the position of the accelerator pedal via two fixed Hall elements. If one Hall element fails, a changeover to the second one takes place. The throttle valve opening is limited to about 60 % of the maximum opening. The throttle valve opening speed is also delayed. If the brake pedal is operated, this always means idle speed input. If the plausibility check of the Hall signals is negative or if both Hall sensors fail, only idle speed is controlled.

Limp-home mode upon failure of actual value potentiometers 

If one actual value potentiometer fails, a changeover to the associated second actual value potentiometer takes place. Air mass is used as an additional comparison value. If both actual value potentiometers malfunction, return springs bring the throttle valves to the limp-home position of about 5° opening angle.

Limp-home mode upon failure of throttle valve actuator motors 

If the throttle valve actuator motors fail, they are de-energized. Return springs move the throttle valves to the limp-home position of about 5° opening angle.

Limp-home mode upon failure of crankshaft Hall sensor 

If the crankshaft Hall sensor fails, the signals of the intake camshaft Hall sensors or those of the exhaust camshaft Hall sensors are used as a substitute.

IMPORTANT Recognized failures or faults are stored in the fault memory and can be read out and deleted using the diagnostic tester.

Limp-home position 

When the throttle valves are in limp-home position, the engine speed is regulated by activation/deactivation of individual cylinders to approx. 1200 to 1400 RPM in neutral, and approx. 1800 RPM when driving. If the brake pedal is operated, this always means idle speed input.

The ME-SFI [ME] control unit controls the shutting off and switching in of the cylinders, depending on:

The ME-SFI [ME] control unit actuates the following components for this purpose:

  Electrical function schematic for engine limp-home mode Engine 177.9 in model 205, 253 PE07.10-P-2719-97FBD
    Engine 177.9 in model 213 up to model year 2021 PE07.10-P-2719-97DBG
  Overview of system components for gasoline injection and ignition system with direct injection Engine 177.9 in model 205, 253 GF07.70-P-9998MNA
    Engine 177.9 in model 213 up to model year 2021 GF07.70-P-9998MNE
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