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

GF07.10-P-1019MI Engine Limp-Home Mode, Function
- as of model year 09

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 deenergized 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.