NOTICE
Do not allow the engine to exceed its governed
speed, or serious engine damage could result.
Apply the service brakes to reduce the engine rpm or
make a slower descent by using a lower gear.
Shutting Down the Engine
Make sure the exhaust brake switch is turned off be-
fore shutting down the engine.
Engine Brake
Engine Brake Switch
The engine brake switch controls the degree of en-
gine braking. Normally there are two paddle
switches, a two-position On/Off Switch to activate the
engine brake, and a two-position Hi-Lo Switch to
control the amount of engine braking.
To turn the two-position On/Off Switch on, raise the
paddle. When the two-position switch is on, an
amber light-emitting diode (LED) illuminates inside
the switch.
To turn the two-position Hi-Lo Switch on high, raise
the paddle. To turn the two-position Hi-Lo Switch on
low, lower the paddle. See
Fig. 13.4.
A three-position switch is used on MBE900 engines
equipped with both the regular engine brake and the
constant-throttle (decompression) brake. It works the
same as the two-position Hi-Lo switch, except that
there is a third (off) position when the switch is left at
its normal position.
When the panel lights are on, the Hi-Lo icon is back-
lit in amber on the three-position switch. On both the
three-position switch and the two-position switch, the
ENG BRK legend is backlit in green when the panel
lights are on.
Constant-Throttle Valves
To increase braking performance, Mercedes-Benz
engines are equipped with optional constant-throttle
valves in each combustion chamber. Small valves
built into the cylinder head allow a small amount of
compressed air to escape through the exhaust port
during the combustion stroke. The constant-throttle
valves are open during the entire time that the en-
gine brake is activated. Although some braking ability
is lost because the valves are constantly open,
constant-throttle braking is quieter in operation than
other types of engine brakes.
When both the exhaust brake and the constant
throttles are installed, a three-position switch on the
dash controls the amount of engine braking deliv-
ered. Like the exhaust brake, the constant throttles
are deactivated when the accelerator or clutch pedal
is depressed. The ABS system, when active, also
deactivates constant-throttle braking.
The engine brake will deactivate if the engine speed
falls below a preset level. This level is program-
mable, but is set at the factory at 1100 rpm.
10/17/2001
f610588
12
1. On/Off Switch 2. Hi-Lo Switch
Fig. 13.4, Engine Brake Switches
Hydraulic and Air Brake Systems
13.7
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