How The Engine Brake Is Activated - Mack Granite GU Series Operator's Handbook Manual

152 OPERATION
To operate the vehicle without the engine brake active, leave the
dash-mounted switch in the OFF position.
CAUTION
The V-MAC® system prevents engine brake activation if the oil temperature is
below 55°C (131°F). The driver should be alert to the fact that the engine brake
will not function until sufficient warm-up time has elapsed, regardless of the dash
switch setting.

How the Engine Brake is Activated

When the engine brake is "enabled" (switch in either LOW or HIGH position),
your engine V-MAC® electronic control system commands engine brake
power (engine brake "active") only when the following conditions are true:
• The foot-operated engine accelerator pedal is not depressed.
• The clutch pedal is not depressed (manual shift transmissions only).
• The engine speed is at least 900 rpm.
• Vehicle must be in gear.
• Vehicle speed should be greater than 8 km/h.
If the engine brake is active, the engine brake will automatically be deactivated
by depressing either the accelerator or the clutch, or if the engine speed drops
below 900 rpm. As soon as all of the engine brake "active" conditions are
again true (taking your foot off the accelerator, for example), the engine brake
will again be activated. In order to disable the engine brake, simply return the
dash-mounted control switch to the OFF position.
DANGER
The engine brake should never be considered a substitute for the vehicle service
brakes. The service brakes should always be maintained in good working order,
and should always be viewed as the primary vehicle slowing system. Service
brakes are always used to bring the vehicle to a complete stop.