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

Engine 178.9 In Model 190 

Function requirements for engine limp-home mode, general points 

IMPORTANT The " Engine running" function requirements include all function sequences of the fuel low pressure and fuel high-pressure circuit, as described in the "Fuel supply" function.

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 (N3/10) controls the engine limp-home mode based on the following sensors and signals:

Function sequence for engine limp-home mode 

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. Throttle valve openings are 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 potentiometer 1 or 2 of the throttle valve actuators on the left and right 

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

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

The throttle valve actuator is de-energized and the throttle valve is set to the limp-home position of an opening angle of approx. 5° by the spring capsule.

Function sequence for limp-home position 

When the throttle valves are in limp-home position, engine speed is limited by cylinder activation/deactivation, to about 1200 to 1400 RPM when at idle, and in driving mode to about 1800 RPM. If the brake pedal is operated, this always means idle speed input.

The ME-SFI [ME] control unit activates/deactivates the cylinders by switching the fuel injectors (Y76) on or off, 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   PE07.10-P-2719-97HBA
  Overview of system components for gasoline injection and ignition system with direct injection   GF07.70-P-9998MNB 
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