GF30.20-P-4026MIS Electronic Accelerator Pedal Emergency Running Mode, Function

GF30.20-P-4026MIS Electronic Accelerator Pedal Emergency Running Mode, Function
- ENGINES 272.9 in MODEL 221.0 /1 as of model year 2009 /YoM 08
- ENGINES 273.9 in MODEL 216.3, 221.0 /1 as of model year 2009 /YoM 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 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.
Limp-home is recognizable from a significantly surging engine running characteristic.

The ME-SFI [ME] 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), engine speed
- Throttle valve actuator (M16/6), throttle valve position
- ESP control unit (N47-5) or regenerative braking system (N30/6) (for hybrid), brake actuation via chassis CAN (CAN E)
- Electric controller unit (VGS) (Y3/8), gear range over the engine compartment (CAN C)

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. 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 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 [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).