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

GF07.10-P-1019OG Engine Limp-Home Mode, Function
ENGINES 642.8 in MODEL 204.0 /2 /9, 207.3 /4, 212.0 /2, 218.3

Function requirements for engine limp-home mode, general points
^ 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 CDI control unit (N3/9) controls engine limp-home mode based on the following sensors and signals:

- Camshaft Hall sensor (B6/1)
- Accelerator pedal sensor (B37), accelerator pedal position
- Crankshaft Hall sensor (B70), engine speed
- 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 used as of 1.3.2011 (model 204.0/2) 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)

Until 28.2.2011 (model 204.0/2) or 31.5.2011 (model 204.9) and as of 1.6.2011 (model 204.9) only the basic variant of the Electronic Stability Program control unit 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 the crankshaft Hall sensor

Function sequence for limp-home mode on failure of the accelerator pedal sensor
In case of failure of a Hall sensor the system switches to a second Hall sensor and the engine power is reduced.
To do this the CDI control unit regulates the fuel pressure in the rails via the pressure regulating valve (Y74) and quantity control valve (Y94) and the injection time through the actuation of the fuel injectors (Y76).

If the plausibility check made by the CDI control unit is negative or if both Hall sensors fail, the system will only work to regulate the idle speed.

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 camshaft Hall sensor will be used instead (for limp-home mode).

Diagnosis
Faults detected by the accelerator pedal sensor are stored in the fault memory and can be read out and erased using Xentry Diagnostics.