DD15 Operator Guide – Cruise Control

Cruise Control

For added driver convenience and comfort, DDEC VI also features a Cruise Control option that works just like the system in your car. It can be operated in any gear above 1100 rpm or road speed faster than 20 mph (32 kph), up to the rated engine speed. It also can be programmed to hold your road speed at or below the maximum vehicle speed. The switch to energize Cruise Control is usually mounted on the instrument panel. ‪

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Turn the switch ON to energize the system. Remember as a check after each engine start, DDEC VI looks for a one time activation of the clutch (if equipped) and service brake before DDEC VI allows Cruise Control to be enabled.‪

DDEC VI must also see or recognize that the Cruise Enable Switch has changed. If the Cruise Enable Switch is OFF it needs to be turned ON. If the Cruise Enable Switch is left in the ON position at key OFF, the switch must be cycled OFF then ON for DDEC VI to see a status change to allow Cruise Control activation. The status of DDEC VI inputs to activate Cruise Control at key ON is listed in Table
“Input Status to Activate Cruise Control”


Once Cruise Control is enabled and you reach your road speed, press the SET Switch to activate Cruise Control. The cruise light will come on. To increase road speed in one mile-per-hour (1.6 kilometer-per-hour) increments, press the RSM/ACC Switch. To reduce road speed, press and hold the SET/CST Switch until the lower speed is reached.‪

Cruise Control is deactivated by slightly pressing the service brakes, clutch pedal, or trailer brake. The ON/OFF Switch will also deactivate Cruise Control. ‪

Cruise Control will maintain vehicle speed even on up grades, unless power requirements demand a downshift. If the Cruise Control/Engine Brake function is turned ON, the Cruise Control will limit your speed on down grades. Most likely, Cruise Control will feel stronger than driving with the accelerator pedal because of the instantaneous and wide-open throttle response. That’s why Cruise Control use is not suggested during slippery driving conditions.‪


Status of Input at Key ON‪

Status of Input Before Cruise Control Activates‪

Service Brake Switch‪



Clutch Release Switch (Manual Trans only)‪



Cruise Control Enable Switch‪



Table 1. Input Status to Activate Cruise Control

Use Cruise Control after down shifting on a hill to pull the hill. Hitting the RSM/ACC Switch (not the SET Switch) will keep the truck accelerating in the lower gears up to the rated engine speed.‪

Cruise Control will disengage below 1000 rpm or 20 mph (32 kph) road speed. When using Cruise Control, if you want to pull the engine below 1000 rpm, remember to hold the accelerator pedal to the floor to keep the engine pulling at wide-open throttle. The engine will pull to about 1050 rpm.‪

The electronic data programmed into the DDEC VI system will not allow you to hurt or overfuel the engine at low or “lug” engine speeds. There is enough oil pressure to withstand hard pulls at low engine speeds. ‪

EPA07 DD15 Operator’s Guide – DDC-SVC-MAN-0003
Generated on 10-13-2008