exhaust port. This brings about the desired
decompression during the power stroke.
When the engine brake is activated, the con-
stant throttle valves are opened. For
OM 904/OM 924 engines, the actuation is
pneumatic. For OM 906/OM 926
engines,
the actuation is hydraulic. The brake valve on
the exhaust gas turbocharger is also closed.
The engine brake is actuated by the FR (drive
control) unit (Y page 23) or the ADM.
The engine brake is always deactivated below
900 rpm. This prevents the engine from stall-
ing. The engine brake is automatically deac-
tivated even if the position sensor (e.g. accel-
erator pedal) is in use.
i
In emergency mode (constant engine
speed), the engine brake can only be acti-
vated in overrun mode at increased engine
speed. Once the constant engine speed is
reached, the engine brake is automatically
deactivated again.
Cold-start aid
The cold-start
aid makes it easier to start the
engine at low outside temperatures (below
–15 †); it is activated when the outside tem-
perature falls below –4 †.
H
Environmental note
At outside temperatures below about –4 †
the cold-start aid minimises emissions (after
starting
the
engine). In addition, it reduces the
load on the starter motor and batteries and
enables the engine to be started more rapidly.
For this reason you should only start the
engine after the % indicator lamp goes out.
X
To activate the cold-start aid: turn the
vehicle key
to the drive position in the igni-
tion lock.
The % indicator lamp lights up in the
instrument panel.
X
After the % indicator lamp goes out,
start the engine within 30
seconds.
The cold-start aid is automatically deactiva-
ted if:
R
the engine
is not started within 30 seconds
of the % indicator lamp going out.
R
the engine is started while the % indi-
cator lamp is still lit.
R
the coolant temperature reaches around
0 † while the engine is running.
At a coolant temperature above approx-
imately –4 †, the % indicator lamp goes
out after approximately 2 seconds (function
check). At a coolant temperature below
approximately –4 †, the % indicator lamp
goes out after approximately 20 seconds.
Have the cold-start aid checked and repaired
at a qualified specialist workshop. Mercedes-
Benz recommends that you use a Mercedes-
Benz or MTU Service Centre for this purpose
(Y page 11). Work relevant to safety or on
safety-related systems must be carried out at
a qualified specialist workshop.
General information
27
At a glance
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