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

ENGINE 275.953 in MODEL 216.376, 221.176 as of Model Year 09 /AEJ 08

ENGINE 275.982 in MODEL 216.379, 221.179 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 position sensor (L5), motor speed
Throttle valve actuator (M16/6), throttle valve position
ETC control unit (N15/3), gear range over the drive train CAN (CAN C)
ESP control unit (N47-5), brake actuation over the chassis CAN (CAN E)

Limp-home mode electronic accelerator function sequence

The function sequence is described in the following steps:

Limp-home mode on failure of the accelerator pedal sensor
limp-home mode function sequence on failure of throttle valve actual value potentiometer 1 or 2 (M16/6r1, M16/6r2)
Limp-home mode function sequence on failure of the throttle valve actuator motor (M16/6m1)
Limp-home position function sequence

Limp-home mode function sequence 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 is negative or if both Hall sensors fail, only idle speed is then still controlled.

Limp-home mode function sequence on failure of throttle valve actual value potentiometer 1 or 2

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 are faulty, the spring capsule brings the throttle valve to the limp-home position of about 10° opening angle.

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

The throttle valve actuator is de-energized and the spring capsule brings the throttle valve to the limp-home position of about 10° opening angle.

Limp-home position function sequence

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 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 by the accelerator pedal sensor and throttle valve actuator 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-2051-97CAA
Function schematic for limp-home electronic accelerator	Model 221	PE30.20-P-2051-97SAA
ME-SFI [ME] control unit, component description	N3/10	GF07.61-P-6000MOS