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

GF07.10-P-1019MAW Engine Limp-Home Mode, Function
ENGINES 156.9 in MODEL 204.0 /2 /3, 212.0 /2

Function requirements for engine limp-home mode, general
^ Circuit 87M (engine timing ON)
^ Engine running

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 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
- Front and rear throttle valve actuator (M16/3, M16/4), throttle valve positions
- Electronic stability program control unit (N30/4) or Premium electronic stability program control unit (N30/7) (on model 212 with DISTRONIC PLUS), brake actuation chassis CAN (CAN - Fully integrated transmission controller unit (Y3/8) gear range, via the drive train CAN (CAN C)

Function sequence for engine limp-home mode
The function sequence is described in the following Operation

^ Function sequence for limp-home mode on failure of the accelerator pedal sensor
^ Function sequence for limp-home mode on failure of throttle valve actual value potentiometer 1 or 2 (M16/3r1, M16/4r1, M16/3r2, M16/4r2)
^ Function sequence for limp-home mode on failure of a throttle valve actuator motor (M16/3m1, M16/4m1)
^ Function sequence for limp-home position
^ Function sequence for limp-home mode on failure of the crankshaft Hall sensor

Function sequence for limp-home mode on failure of the accelerator pedal sensor
If a Hall sensor fails, the system switches over to the second Hall sensor. Throttle valve openings are limited to about 60 % of the maximum opening. Throttle valve opening speeds are also limited dynamically (delayed opening of throttle valves).

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 on 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 throttle valve actuators are switched off and the spring capsules set the throttle valves to the limp-home position of about 10° opening angle.

Function sequence for limp-home mode on failure of a throttle valve actuator motor
The throttle valve actuators are switched off and the spring capsules set the throttle valves to the limp-home position of about 10° opening angle.

Function sequence for limp-home position
When the throttle valves are in limp-home position, engine speed is limited by cylinder activation/deactivation, to about 1200 to 1400 rpm when at idle, and in driving mode to about 1800 rpm. 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
- Selected gear range

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).

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