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

Engine 176.9, 177.9 in model 217 

Engine 176.9, 177.9 in model 222 

Engine 177.9 in model 290 

up to model year 2021 

Function requirements for engine limp-home mode, general points 

Engine limp-home mode, general 

The task of engine limp-home mode is to ensure continued safe driving in the case of malfunctions of individual component parts of the engine management.

The ME-SFI [ME] control unit (N3/10) controls the engine limp-home mode based on the following signals:

Function sequence for engine limp-home mode 

The function sequence for engine limp-home mode is described using the following subfunctions:

Function sequence for limp-home mode for failure of the accelerator pedal sensor 

If a Hall sensor fails, the system switches over to the second Hall sensor. The throttle valve opening is limited to about 60% of the maximum opening. Throttle valve opening speeds are also limited dynamically (delayed opening of throttle valves). If the brake pedal is operated, this always means idle speed input. If the plausibility check for the Hall sensor signals is negative or if both Hall sensors fail, only idle speed is then still controlled.

Function sequence for limp-home mode in the event of failure of the left and right actual value potentiometers 1 or 2 

If one potentiometer fails, the other potentiometer is used. Air mass is used as an additional comparison value. If both potentiometers are defective, the return springs bring the throttle valves to the limp-home position of approx. 5° opening angle.

Function sequence for limp-home mode in the event of failure of the left and right throttle valve actuator motors 

The throttle valve actuators are switched to a deenergized state and the return springs bring the throttle valves to the limp-home position of approx. 5° opening angle.

Function sequence for limp-home position 

When the throttle valves are in limp-home position, fuel is shut off/switched-in again to the cylinders to limit engine speed to about 1200 to 1400 rpm at idle and about 1800 rpm in driving mode. If the brake pedal is operated, this always means idle speed input.

Cylinder shutoff and activation is done by the ME-SFI [ME] control unit by activating and deactivating the fuel injectors of cylinders 1 to 8 (Y76/1 to Y76/8) depending on:

Function sequence for limp-home mode on failure of the crankshaft Hall sensor 

If the voltage signal from the crankshaft Hall sensor fails the voltage signals from the intake camshaft or exhaust camshaft Hall sensor are used as replacement (for limp-home mode).

IMPORTANT Faults recognized at the accelerator pedal sensor, left and right throttle valve actuator, crankshaft Hall sensor, left and right intake camshaft Hall sensor and left and right exhaust camshaft Hall sensor are stored in the fault memory and can be read out and deleted with Xentry Diagnostics.

  Electrical function schematic for engine limp-home mode Engine 177.9 in model 290 up to model year 2021 PE07.10-P-2719-97XBA
    Engine 176.9, 177.9 in model 217Engine 176.9, 177.9 in model 222 PE07.10-P-2719-97SEL
  Overview of system components for gasoline injection and ignition system with direct injection   GF07.70-P-9998MNL 
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