Audi 4.2-litre V8 FSI, Service Training

Page: 44 / 48

44
377_070
Engine management
Start mode of the Audi RS4
Start button
(starter button E378)
The RS4 is equipped with a Start button (except
models for USA, Canada and Korea).
It is located in the centre console adjacent the
handbrake lever. The engine is started by briefly
pressing the switch when the ignition is "on".
The Start button is a simple NO contact and
switches the terminal 15 signal through to the
engine control unit J623 when terminal 15 is
actuated.
Apart from the fact that the start contact has been
moved to the Start button, the functions of the
ignition lock are the same as in the A4. The ignition
lock is disabled in the starting position.
To start the engine, the signals from the clutch
pedal switch F36 and the clutch pedal switch for
engine starting F194 must also be present.
When the clutch is depressed, the F36 recognises
that the clutch pedal has left its rest position and
opens.
The F194 is actuated, i.e. closed, when the clutch is
fully depressed.
Because one switch opens and the other closes, the
engine control unit can verify the redundancy of
both switches.
The cruise control system also utilises the signal
from the F36.
When a repeat attempt is made to start the
(e. g. stalled) engine, the ignition key does not have
to be turned back. The vehicle can be restarted
straight away.
Operating the Start button when the engine is
running has no effect as the Start button is disabled
by the engine control unit when engine RPM is
detected.
By alternately switching off the starter relay after
engine start, the engine control unit can determine
whether either of the two relays is "sticking".
Function testing both relays ensures that the starter
is always switched off after engine start and there-
fore de-meshes.
If a relay does fails to open due to "sticking", current
flow is nevertheless interrupted by the opening of
the second relay. In this case a fault is entered in the
engine control unit memory.