Electronic accelerator emergency running function

Pedal value sensor emergency running

If a potentiometer fails, the system switches over to the second potentiometer. The throttle valve opening is limited to about 60%. In addition, the throttle valve opening rate is limited dynamically, the throttle valve opens with a time lag (EPC malfunction indicator lamp does not come on).

If the plausibility check produces a negative result or if both potentiometers are faulty, only idle speed is then still controlled (EPC malfunction indicator lamp comes on).

Actuator emergency running - electric

If a potentiometer fails, the system switches over to the second functioning potentiometer. The fuel injection system makes use of the air mass value as an additional comparison parameter. After a plausibility check, the throttle valve opening is limited to about 60% in line with engine speed and load (EPC malfunction indicator lamp does not come on).

If the plausibility check produces a negative result or if both potentiometers are faulty, a faulty actuator is then no longer operated. Consequently, the throttle valve adopts a mechanical emergency running position which is fixed by the spring capsule in the actuator (EPC malfunction indicator lamp comes on).

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Actuator emergency running - mechanical emergency running stop

If the servo motors or actuators are faulty, both actuators are de-energized. The throttle valves are resting against the mechanical stop (spring capsule) as a result of this the throttle valve opening is a constant 10–12°. At no engine load (idling) engine speed of about 900 rpm is controlled by switching the cylinders off and on.

When driving, engine speed is controlled by switching the cylinders off and on at the fuel end, depending on engine load. Maximum engine speed is about 1800 rpm and is fixed by the mechanical stop (EPC malfunction indicator lamp comes on).

If only one actuator is faulty, the relevant bank of cylinders operates only up to about 1800 rpm for stabilizing idle speed. The fuel injection valves are no longer actuated beyond this speed. A throttle valve opening of up to about 100% is possible in the case of the fault-free bank of cylinders (EPC malfunction indicator lamp comes on).

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Safety fuel shutoff

If a mechanical fault exists in an actuator, fuel injection at the relevant bank of cylinders is shut off. If both actuators have a mechanical fault, the safety fuel shutoff is activated.

In this case, the fuel injection valves are switched off at engine speeds of about >1400 rpm and operated again at about
<1200 rpm (EPC malfunction indicator lamp comes on).

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If the faults described above exist, read the fault memory. The EPC malfunction indictor lamp was installed only on model 129, 140 from about 4/95 up to about 5/96.

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