Brake - Auxiliary; Brake - Engine - Holiday Navigator 2003 Owner's Manual

Chassis Information
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BRAKE -
AUXILIARY

Brake - Engine

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Auxiliary braking systems are designed to supplement the standard wheel
braking system. These devices are not designed to bring the motorhome to a
complete stop; however, they can assist in controlling the speed of the
motorhome. Use of the engine braking system can save on costly service brake
repairs.
The "Jake" brake is an engine-braking device that operates on a different
principle than an exhaust brake. An engine brake functions by releasing the
engine's compression. The effect of the engine brake increases with engine
speed. When the engine brake is activated the Allison transmission automatically
downshifts, utilizing the gear selected and maximizing the engine braking
effect.
When the engine brake activates, an electrical signal is sent to the engine's
ECM (electronic control module). The ECM controls a hydraulic circuit that
opens the exhaust valves near the end of the compression stroke. The potential
engine braking power depends on turbocharger boost pressure, engine speed,
compression ratio, injector timing and when the exhaust valves open.
Located on the driver's left console is a brake switch and a HI/LOW switch.
The HI/LOW switch allows for the selection of different levels of engine
braking power. Selecting "LOW" activates the engine brake on three cylinders.
Selecting the "HI" setting activates the engine brake on six cylinders.
The engine brake will not be enabled when:
• The cruise control is active.
• The engine speed goes below 850 RPM.
• An electronic fault code is active.
The throttle sensor is a component part of the accelerator pedal assembly
and deactivates the engine brakes when the throttle is applied. Applying the
service brakes while in cruise control will disengage the cruise control and
enable engine brake. The Jake Brake foot switch (some models) will not
disengage the cruise control. Use the Jake Brake when going down a hill,
freeway or off ramp. The engine brake will allow the engine temperature to
drop while going downhill.
NOTE: Idle the engine three to five minutes at approximately
1000 RPM to warm the engine before activating the engine brake.
Do not operate the engine brake until the engine oil temperature is
above 30º C (86º F).
WARNING: The engine brake is designed to assist the motorhome
service brakes.
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