The function diagram for the SCCS includes the following:
• Electronic System Controller (ESC)
• Electronic Control Module (ECM)
• Steering wheel cruise control switches
Cruise Control
The ECM will control engine speed to maintain a constant road speed with cruise control. Pressing the set switch when the vehicle is at the desired speed with the CRUISE switch in the on position activates the cruise control. Speed is increased or decreased by pressing ACCEL/CRUISE switches. The cruise control is deactivated by pressing the off switch, applying the brake pedal, clutch pedal, or on vehicles equipped with automatic transmissions, by placing
the transmission in neutral.
Power Takeoff (PTO) Control
Engine speed can be controlled by the SCCS switches if the PTO option has been programmed into the
ECM and the vehicle is stationary. Variable as well as preset speeds are available depending on ECM programming. The PTO function is turned on by pressing the cruise switch on. Pressing the SET/CRUISE or RESUME/ACCEL switches will increase or decrease engine speed depending on PTO programming.
SCCS Circuit Operation
Cruise control allows the ECM to control the engines power delivery to maintain a constant vehicle speed.
The speed set point is determined by the operator and the cruise high and low set points are programmed in the ECM. The minimum engine speed that the cruise control can be engaged is programmed in the ECM.
In-Cab PTO
In-Cab PTO has three different modes of operation.
These modes are selected by programming the ECM In-Cab PTO Mode. These modes are:
• In-Cab Preset
• In-Cab Variable
• In-Cab Mobile
In-Cab Preset
In-Cab Preset is selected by programming the ECM programmable parameters for In-Cab Mode to In-Cab
Preset. This allows the operator to select one of two programmed values for engine speed. To operate, press the ON/OFF switch to the ON position. Then press either the SET/CRUISE or RESUME/ACCEL switch. This will cause the engine speed to run at the value programmed into PTO Set Speed.
Pressing the off switch, brake pedal, clutch pedal, placing the automatic transmission in gear, or a signal from the Vehicle Speed Sensor (VSS) (unless programmed for Mobile operation), will deactivate the PTO speed control. PTO speed control will not be functional if the VSS signal is in fault.
In-Cab Variable
In-Cab Variable is selected by programming the ECM Programmable Parameters for In-Cab Mode to In-Cab Variable. This option allows the operator to set the engine speed to a desired value. The control module will then maintain this speed over varying load conditions up to the engines rated power in the selected speed range.
To enable, press the ON/OFF switch to the ON position. Speed may be adjusted two ways. First the operator may adjust the engine speed with the accelerator and then press the SET/CRUISE switch.
Second, the operator may press the RESUME/ACCEL to increase engine speed incrementally or press the SET/CRUISE switch to decrease the engine speed.
Engine set speed will be limited to the value programmed in the ECM for Maximum PTO speed.
Pressing the OFF switch, brake pedal, clutch pedal, placing the automatic transmission in gear, or a signal from the VSS, (unless programmed for Mobile operation), will deactivate the PTO speed control. PTO speed control will not be functional if the VSS signal is in fault.
In-Cab Mobile
In-Cab Mobile is selected by programming the ECM programmable parameters for the In-Cab mode to In-Cab Mobile. This allows the operator to use the engine speed control the same as In-Cab Variable, however, in this mode the vehicle can be moving while the mode is active. See In-Cab Variable for more details. The maximum speed of the vehicle is programmable up to 20 mph. This mode is the same as In-Cab Variable, however, a speed signal will not disable the speed control until the programmed maximum speed is exceeded.
Remote PTO
Remote PTO can be enabled by two means, Remote Preset and Remote Variable. Operation of the speed control depends on which signal is enabled.
Remote Preset
When in the preset mode, the set switch will cause the engine to run at the programmed set speed. The RESUME/ACCEL switch will allow the engine to run at the programmed resume speed.
With the remote preset enabled, the speed is adjusted as with In-Cab preset. See In-Cab preset for more details.
Turning the ON/OFF switch OFF, depressing the brake pedal, clutch pedal, placing the automatic transmission in gear, or a signal from the VSS will deactivate the PTO speed control. However, the programmed option of PTO Operation Disable will prevent the clutch and brake signals from interrupting the PTO speed control, as well as cause the Accelerator Position Sensor (APS) to be inoperative. PTO speed control will not be functional if the VSS signal is in fault.
Remote Variable
Enabling the remote variable signal allows for the engine speed to be adjusted to the desired level.
Pressing the RESUME / ACCEL switch will cause the engine speed to increase, pressing the SET/CRUISE switch will cause the engine speed to decrease.
With remote variable enabled the speed is adjusted as with In-Cab Variable.
Opening the switch to Pin X3–20, pressing the ON/OFF switch to OFF, depressing the brake or clutch pedal or placing the automatic transmission in gear, or a signal from the VSS will deactivate the PTO speed control. However the programmed option of PTO Operation Disable will prevent the clutch and brake signals from interrupting the PTO speed control, as well as cause the APS to be inoperative.
PTO speed control will not be functional if the VSS signal is in fault.
PTO Speed Ramp Rate
The rate at which the speed of the engine will change will depend on load conditions and on a programmed value called PTO speed ramp rate. A higher value will cause the engine to change speed more quickly.
Tools
• EST with INTUNE and MasterDiagnostics® software
• EZ-Tech® interface cable
• Electrical System Troubleshooting Guide (truck manual)
• Electrical Circuit Diagrams (truck manual)
Fault Detection / Management
The ECM does not monitor the SCCS system for faults.
There are no Diagnostic Trouble Codes (DTCs) for this system.
Diagnostics
If the engine does not respond to the cruise control switches, use INTUNE to monitor cruise switch input to the ESC. If the switch state does not change when the cruise controls are pressed, diagnose the cruise switch circuits using the Electrical System Troubleshooting Guide. If the ESC is receiving the cruise switch input, use MasterDiagnostics®
to view the cruise switch state. If the switch state does not change as the switch is pressed, verify communication exists between the ECM and the ESC (does the ECM respond to other ESC inputs). If the switch state does change, verify that other conditions do not exist that would stop or delay the reaction to the input. Examples include:
• rpm below minimum
• rpm above maximum
• Road speed below minimum / Road speed above maximum
• Brake pedal depressed
• Clutch / driveline disengaged
The EST can be used to monitor the status of the PTO controls. Comparing the data list reading to actual operation will indicate if the controls are operating correctly. Using the menu option of programmable parameters the programming can be verified to be sure the ECM is programmed correctly for the application. Also the data list can be used to monitor the parameters that cause interruption of PTO speed control.
