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

ENGINE 281.910 in MODEL 453.0/3/4 

Function requirements for engine limp-home mode, general points 

• Circuit 87 (Engine management ON)
• Engine runs

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:

• Intake camshaft Hall sensor (B6/15), intake camshaft setting
• Accelerator pedal sensor (B37), accelerator pedal position
• Crankshaft position sensor (L5), engine speed
• Throttle valve actuator (M16/6), throttle valve position
• Brake light switch (S9/1), status

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 
• Function sequence for limp-home mode in the event of failure of actual value potentiometer 1 (M16/6r1) or actual value potentiometer 2 (M16/6r2) of throttle valve actuator 
• Function sequence for limp-home mode in the event of failure of throttle valve actuator motor (M16/6m1) 
• Function sequence for limp-home position 
• Function sequence for limp-home mode for failure of the crankshaft position sensor 

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 in the event of failure of actual value potentiometer 1 or 2 of throttle valve actuator 

If one potentiometer fails, the other potentiometer is used. If both potentiometers are defective, the return spring brings the throttle valve to the limp-home position with a small opening angle.

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

The actuator motor is deenergized and the throttle valve is set to the limp-home position with a small opening angle by the return spring.

Function sequence for limp-home position 

For a throttle valve in the limp-home position the engine rpm is regulated by the fuel-side cylinder switching off and switching-in in neutral to a low rotational speed and in driving mode to a medium rotational speed. If the brake pedal is operated, this always means idle speed input.

Switching on and off of the cylinder takes place by the ME-SFI [ME] control unit through switching of and switching-in of cylinder 1 injection valve (Y62/1) to cylinder 3 injection valve (Y62/3), dependent on:

• Engine speed
• Accelerator pedal input

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

If no voltage signal is received from the crankshaft position sensor, the voltage signal from the intake camshaft Hall sensor is used instead (for limp-home mode). The limp-home mode rpm lies at a max. 3000 rpm.

Diagnosis

Recognized errors on the accelerator pedal sensor, throttle valve actuator, crankshaft position sensor and intake camshaft Hall sensor are stored in the fault memory and can be read out and deleted using Xentry Diagnostics.

	Electrical function schematic for engine limp-home mode		PE07.10-P-2719-97BBA
	Overview of system components motor electronics (ME-SFI) fuel injection and ignition system		GF07.61-P-9997KJ