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

GF07.10-P-1019MM Engine Limp-Home Mode, Function
ENGINES 276.9 in MODEL 204.0 /2 /3 /9, 207.3 /4, 212.0 /2, 218

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

- 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) (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 Stability Program control unit (N30/4) will be introduced into service as of 1.3.2011 (model 204.0/2) or as of 1.6.2011 (model 204.3) in 2 variants:
- Electronic Stability Program control unit, basis variant (except code (233) DISTRONIC PLUS)
- Electronic Stability Program control unit, Premium variant (except code (233) DISTRONIC PLUS)

From 1.6.2011 only the basic variant of the Electronic Stability Program control unit will be used in model 204.9.

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 brake pedal is actuated this always means an idle specification. If the plausibility checking of the Hall sensor signals is negative or if both Hall sensors failed, then only the idle speed

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 5° opening angle.

The position feedback of the throttle valve actuator takes place by means of a contact-less angular sensor.

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. 5° 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 on / off(Y76) dependent on the engine rpm and the accelerator request.

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 recognized on the accelerator pedal sensor, throttle valve actuator, crankshaft Hall sensor, left and right intake camshaft Hall sensor and left and right exhaust camshaft Hall sensor are stored in the fault memory and can be read out and erased with Xentry diagnosis.