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Engine limp-home mode, function - GF07.10-P-1019MM

ENGINE 276.9 in MODEL 204 

ENGINE 276.9 in MODEL 207, 212 (except 212.095), 218 up to model year 2014 

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 timing system.

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 

The function sequence is described in the following steps:

Function sequence for limp-home mode on failure of 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 faulty, 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 switched in a deenergized state and the throttle valve is set to the limp-home position at 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 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 on 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 erased with Xentry diagnosis.

  Electrical function schematic for engine limp-home mode MODEL 204 PE07.10-P-2719-97FAK
MODEL 207 PE07.10-P-2719-97EAH
MODEL 212 PE07.10-P-2719-97DAI
Model 218 PE07.10-P-2719-97XAB
  Overview of system components for gasoline injection and ignition system with direct injection ENGINE 276.9 in MODEL 204
ENGINE 276.9 in MODEL 207, 212 (except 212.095), 218 up to model year 2014		 GF07.70-P-9998MM
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