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

ENGINE 272.9 (except 272.98) in MODEL 204.0 /2 as of model year 2009 /YoM 08 

ENGINE 272.9 (except 272.98) in MODEL 204.9, 207.3 /4, 212.0 /2 

ENGINE 273.9 in MODEL 207.3 /4, 212.0 /2 

Function requirements for engine limp-home mode - general points 

• Circuit 87M ON (engine control ON)
• Engine running

Engine limp-home mode, general points 

The task of engine limp-home mode consists of ensuring secure further driving in the case of faults on individual components of the engine control.

The ME-SFI [ME] control unit (N3/10) controls engine limp-home mode according to the following sensors and signals:

• LH and RH intake camshaft Hall sensor (B6/4, B6/5), intake camshaft positions
• LH and RH exhaust camshaft Hall sensor (B6/6, B6/7), exhaust camshaft positions
• Accelerator pedal sensor (B37), accelerator pedal position
• Crankshaft Hall sensor (B70), engine speed
• Throttle valve positioner (M16/6), throttle valve position
• Electronic Stability Program control unit (N30/4) or Electronic Stability Program Premium control unit (N30/7) (for DISTRONIC PLUS), brake actuation via the chassis CAN (CAN E)
• Fully integrated transmission control controller unit (Y3/8), gear range via the drive train CAN (CAN C) (for an automatic transmission)

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

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 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 10° opening angle.

Limp-home mode function sequence on failure of the throttle valve actuator motor 

The throttle valve actuator is switched in a de-energized state and the throttle valve is set to the limp-home position at an opening angle of approx. 10° 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 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 injection valves (Y62) on or off, depending on:

• Engine speed
• Brake recognition
• Engaged gear range (for automatic transmission)

Function sequence for limp-home mode for 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).

Diagnosis

Faults detected on the accelerator pedal sensor and the throttle valve positioner are stored in the fault memory and can be read out and deleted with the Xentry diagnostic system.

	Component description for ME-SFI [ME] control unit	N3/10 Engine 272	GF07.61-P-6000MI
	Component description for Electronic Stability Program control unit	N30/4 Model 204.0/2/9	GF42.45-P-5119CE
	Component description for fully integrated transmission control unit	Y3/8n4 Model 204.0/2/9 for transmission 722.9	GF27.60-P-5165AHW