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

GF07.10-P-1019MG Engine Limp-Home Mode, Function
ENGINES 271.8 in MODEL 204.0 /2 /3, 207.3 /4, 212.0 /2

Function requirements for engine limp-home mode, general points
^ Circuit 87 M ON (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 control system.

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

- Intake camshaft Hall sensor (B6/15), intake camshaft setting
- Exhaust camshaft Hall sensor (B6/16), exhaust camshaft setting
- 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) (except code (233) DISTRONIC PLUS) or Electronic Stability Program Premium control unit (N30/7) (for code (233) DISTRONIC PLUS), brake actuation via the chassis CAN (CAN E)
- The electronic transmission control control unit (N15/3) (for code (423) 5-speed automatic transmission (NAG)) or fully integrated transmission control controller unit (Y3/8) (for code (427) 7-speed automatic transmission), gear range via the drive train CAN (CAN C)

The Electronic Stability Program control unit (N30/4) will be introduced into service as of 1.3.2011 (model 204.0/2) or as of
- Electronic Stability Program control unit, basis variant (except code (233) DISTRONIC PLUS)
- Electronic Stability Program control unit, Premium variant (except code (233) DISTRONIC PLUS)

Up to 28.2.2011 or 31.5.2011 only the Electronic Stability Program control unit Basis variant will be used.

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 the accelerator pedal sensor
^ Function sequence for limp-home mode 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 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. 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.

Function sequence for limp-home mode 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 fuel injectors (Y76) on or off, depending on:

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

Function sequence for limp-home mode on failure of the crankshaft Hall sensor
If no voltage signal is received from the crankshaft Hall sensor, the voltage signal from the intake camshaft or exhaust camshaft Hall sensor is used instead (for limp-home mode).

Diagnosis
Faults detected by 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.