Electronic accelerator pedal emergency running mode, function - GF30.20-P-4026MAS

ENGINE 156.984 in MODEL 216.377, 221.077 /177 as of Model Year 09 /AEJ 08

Electronic accelerator limp-home mode function requirements, general

Circuit 87M ON (engine control ON)
Engine running

Limp-home mode electronic accelerator, general points

The task of the electronic accelerator (EFP) limp-home mode consists in ensuring that the vehicle can be continued to be driven safely even if there are faults in the electronic accelerator system (EA).

Limp-home is recognizable from a significantly surging engine running characteristic.

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

Accelerator pedal sensor (B37), accelerator pedal position
Crankshaft Hall sensor (B70), motor speed
Front and rear throttle valve actuator (M16/3, M16/4), throttle valve positions
ESP control unit (N47-5), brake actuation over the chassis CAN (CAN E)
Electric controller unit (VGS) (Y3/8), gear range over the drive train CAN (CAN C)

Limp-home mode electronic accelerator function sequence

The function sequence is described in the following steps:

Limp-home mode function sequence if accelerator pedal sensor fails
Limp-home mode function sequence if actual value potentiometer 1 or 2 (M16/3r1, M16/4r1, M16/3r2, M16/4r2) of a throttle valve fails
Limp-home mode on failure of a throttle valve actuator motor (M16/3m1, M16/4m1), function sequence
Limp-home position function sequence

Limp-home mode function sequence if accelerator pedal sensor fails

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 is negative or if both Hall sensors fail, only idle speed is then still controlled.

Limp-home mode function sequence if actual value potentiometer 1 or 2 of a throttle valve fails

If one potentiometer fails, the system switches over to the second, intact potentiometer. The air flow mass serves as a second parameter for comparative purposes.

If both potentiometers fail, the throttle valve actuators are switched off and the throttle valves are set in the limp-home position of about 10° opening angle by their spring capsules.

Limp-home mode on failure of a throttle valve actuator motor, function sequence

The throttle valve actuators are switched off and the throttle valves are set in the limp-home position of about 10° opening angle by their spring capsules.

Limp-home position function sequence

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 control unit activates/deactivates the cylinders by switching the injection valves (Y62) on / off, according to:

Engine speed
Brake recognition
Selected gear range

Diagnosis

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

Function schematic for limp-home electronic accelerator	Model 216	PE30.20-P-2051-97CAC
Function schematic for limp-home electronic accelerator	Model 221	PE30.20-P-2051-97SAC
ME-SFI [ME] control unit, component description	N3/10	GF07.61-P-6000MAS