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

ENGINE 276.8 in MODEL 292 

ENGINE 276.8/9 in MODEL 166 (except 166.063) 

as of model year 2016 

Function requirements for engine limp-home mode, general points 

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 signals:

Function sequence for engine limp-home mode 

The function sequence is described in the following steps:

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. In addition, the speed at the which the throttle valve opens is dynamically limited (throttle valve opens with a delay). 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 for failure of throttle valve actual value potentiometer 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 spring capsule brings the throttle valve to the limp-home position of about 5°opening angle.

IMPORTANT The position feedback of the throttle valve actuator takes place by means of a contact-less angular sensor.

Function sequence for limp-home mode for failure of the throttle valve actuator motor 

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 valve is in limp-home position, fuel is shut off/resupplied 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.

The ME-SFI [ME] control unit activates/deactivates the cylinders by switching in 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 Diagnosis

Faults recognized at the accelerator pedal sensor, 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-2719-97NBG
  Overview of system components for gasoline injection and ignition system with direct injection ENGINE 276.8 in MODEL 166 (except 166.063)
as of model year 2016
ENGINE 276.8 in MODEL 292		 GF07.70-P-9998MMX
    ENGINE 276.9 in MODEL 166
as of model year 2016		 GF07.70-P-9998MNG
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