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

ENGINE 273 in MODEL 463.202/222/236/237 up to 31.5.12 as of Model Year 2009/YoM 08

Fig 1: Identifying Electronic Accelerator Pedal Emergency Running Mode Function Diagram

Courtesy of MERCEDES-BENZ USA

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 limp-home mode consists in ensuring that the vehicle can continue 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 [ME] control unit actuates the limp-home mode on the basis of the following sensors and signals:

Accelerator pedal sensor, accelerator pedal position
Crankshaft Hall sensor, engine speed
Throttle valve actuator, throttle valve position
ESP control unit, brake actuation via the drive train CAN
Electric controller unit (VGS), gear range via the drive train CAN

Limp-home mode electronic accelerator function sequence

The function sequence is described in the following items:

Limp-home mode on failure of the accelerator pedal sensor
Function sequence for limp-home mode for a failure of the throttle valve actual value potentiometer (M16/6r1) or the drive actual value potentiometer (M16/6r2) for the throttle valve
Limp-home mode function sequence for 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.

Function sequence for limp-home mode for a failure of the throttle valve actual value potentiometer or the drive actual value potentiometer for the throttle valve

If one potentiometer fails, the system switches over to the second, intact potentiometer. 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 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 n = 1200 to 1400 rpm at idle, and about n = 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 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).

Component description for ME-SFI [ME] control unit	N3/10	GF07.61-P-6000G
Component description for ESP control unit	N30/4	GF42.45-P-5118G
Component description for fully integrated transmission control unit	Y3/8n4	GF27.60-P-5165GGA