In the engine start/stop pushbutton (S10.1) are 2 switches, and their applied positions are read in and evaluated by the MR/PLD control unit.
Operating the engine start/stop pushbutton (S10.1) has different effects, depending on which of the two switches is operated, and whether the engine is running or not.
1 Task of the engine start/stop pushbutton (S10.1) when the engine is stopped:
The engine can be started by operating the starter switch at engine start/stop pushbutton (S10.1), for example if the cab is tilted.
In service operations, if the starter switch is operated at the same time as the stop switch, the engine is cranked without starting, as this interrupts actuation of the solenoid valves in the unit pumps.
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A safety feature of the software in the MR/PLD control unit and FR control unit prevents the engine being started if a gear is engaged (starter protection function), or the starter being actuated if the engine is already running (starter locking).
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2 Task of the starter switch at the engine start/stop pushbutton switch (S10.1) when the engine is running:
If the starter switch at the engine start/stop pushbutton switch (S10.1) is operated with the engine running, the MR/PLD control unit increases the idle speed continuously until the engine reaches limit speed or until the starter switch is released again. Once the starter switch is released, the engine control (MR) immediately brings reduces the idle speed again.
As the MR/PLD control unit detects that the engine is running, it prevents the starter from being actuated (starter locking).
3 Task of the stop switch (S10.1), irrespective of whether the engine is running or not:
If the stop switch at the engine start/stop pushbutton (S11) is operated, the MR/PLD control unit stops the actuation of the solenoid valves in the unit pumps, irrespective of whether the engine is running or not.
The entire quantity of fuel delivered between top and bottom dead center by the plunger-and-barrel assemblies in the unit pumps is forced into the diversion chamber concerned, and then into the return duct. Since ejection pressure is not reached at the injection nozzles, fuel injection does not take place and the engine either stops or will not start.
This allows the engine to be switched off, and to be cranked without starting in service operations by operating the start switch and stop switch at the same time.
To avoid switching off the engine inadvertently, the stop switch must be pressed and held until the engine stops or engine speed goes below 50 rpm. If the stop switch is released before then, the engine starts again.