Engine limp-home mode, function - GF07.10-P-1019OGG

ENGINES 642.8 in MODEL 164.1 as of model year 2009/YoM 08 model refinement package 

ENGINES 642.8 in MODEL 164.8, 251.1 as of model year 2009/YoM 08 

ENGINES 642.8 in MODEL 251.0/1 as of model year 2011/YoM 10 model refinement package 

Function requirements for engine limp-home mode, general points 

• Circuit 87 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 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
• ESP control unit (N47-5), brake actuation via engine compartment CAN (CAN-C)
• Electric controller unit (VGS) (Y3/8), gear range via engine compartment CAN

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 
• Function sequence for limp-home mode in the case of failure of the crankshaft Hall sensor 

Limp-home mode function sequence on failure of the accelerator pedal sensor 

In the case of failure of a Hall sensor, switchover takes place to the 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 the injection time over actuation of the fuel injectors (Y76).

If the plausibility check o the CDI control unit is negative or if both Hall sensors fail, only idle speed is then still controlled.

Function sequence for limp-home mode in the case of 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 is used as a substitute (for emergency mode).

Diagnosis

Faults detected by the accelerator pedal sensor and are stored in the fault memory and can be read out and deleted using the Diagnosis Assistance System (DAS).

	Electrical function schematic for engine limp-home mode	Model 164	PE07.10-P-2719-97MAA
		Model 251	PE07.10-P-2719-97RAA
	Component description for CDI control unit	N3/9	GF07.16-P-6000OGU
	Component description for ESP control unit	N47-5	GF42.45-P-5118GM
	Component description for fully integrated transmission control unit	Y3/8n4	GF27.60-P-5165AHZ