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

GF07.10-P-1019MMC Engine Limp-home Mode, Function
- ENGINES 157.9 in MODEL 216.3, 221.0 /1
- ENGINES 278.9 in MODEL 216.3, 221.0 /1

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 the engine limp-home mode consists of ensuring continued safe driving in the case of malfunctions on individual components of the engine control system.

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 sensors (B6/4, B6/5), intake camshaft positions
- LH and RH exhaust camshaft Hall sensors (B6/6, B6/7), exhaust camshaft positions
- Accelerator pedal sensor (B37), accelerator pedal position
- Crankshaft Hall sensor (B70), engine speed
- Throttle valve actuator (M16/6), throttle valve position
- ESP control unit (N47-5), brake actuation via the chassis CAN (CAN E)

Function sequence for engine limp-home mode
The function sequence is described in the following steps:
- Limp-home mode on failure of the accelerator pedal sensor
- limp-home mode function sequence on failure of throttle valve actual value potentiometer 1 or 2 (M16/6r1, M16/6r2)
- Function sequence for limp-home mode on failure of the throttle valve actuator motor (M16/6m1)
- Function sequence for limp-home position
- Function sequence for limp-home mode in the case of failure of the crankshaft Hall sensor

Limp-home mode on 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 of the Hall sensor signals is negative or if both Hall sensor have failed, only the idle speed is then still controlled.

Function sequence for limp-home mode on failure of throttle valve actual value potentiometer 1 or 2,
If one potentiometer fails, the system switches over to the second, intact potentiometer. 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.

Function sequence for limp-home mode on failure of the throttle valve actuator motor
The throttle valve actuator is de-energized and the spring capsule brings the throttle valve to the limp-home position of about 5° opening angle.

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 fuel injectors (Y76) on or off, depending on:
- Engine speed
- Accelerator pedal input

Function sequence for limp-home mode in the case of 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 a replacement (for limp-home mode).

Diagnosis
Recognized errors on the accelerator pedal sensor, throttle valve actuator, crankshaft Hall sensor, LH and RH inlet camshaft Hall sensor and LH and RH exhaust camshaft Hall sensor are stored in the fault memory and can be read and deleted using the DAS.