Speed Control command Switches (SCCS) include cruise control, PTO, and the hand throttle system, see Figure
“Speed Control Command Switches Function Diagram”
.
Figure 1. Speed Control Command Switches Function Diagram
Section 40.1.1
Cruise Control
The ECM will control the engine speed to maintain a constant road speed with cruise control. Depressing 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 depressing Accel or Coast. The cruise control is deactivated by depressing the OFF switch, brake pedal, clutch pedal or on vehicles equipped with automatic transmissions by placing the transmission in neutral.
Section 40.1.2
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 dependent upon programming. The PTO function is turned ON by switching the cruise switch on. Depressing the Set/Coast or Resume/Accel switch will increase or decrease speed dependent upon PTO programming.
Section 40.1.3
Fault Detection Management
The ECM monitors the SCCS signals for proper voltages and will set Flash Code 221. If the ignition switch is turned off, the fault will be recorded as an inactive fault. For circuit 541 and 545 wiring recommendations, see Figure
“Circuit 541 and Circuit 545 Wiring Recommendation “
. For circuit 544 wiring recommendations, see Figure
“Circuit 544 Wiring Recommendation”
.
Figure 2. Circuit 541 and Circuit 545 Wiring Recommendation
Figure 3. Circuit 544 Wiring Recommendation
In cab control switch circuit voltage checks are made with the switch assembly removed from the dash panel. Test from the rear of the connector body. Cruise PTO ON/OFF Switch checks are listed in Table
“Cruise PTO SET/RESUME Switch (COO Switch ON)”
. Cruise PTO SET/RESUME Switch checks are made with the COO switch on and are listed in Table
“Cruise PTO ON/OFF Switch”
.
| Test Points | Spec | Comments |
| 439C to Grd | 12v ± 1.5v | Switch in OFF position – possible open fuse F6 or open circuit. |
| 544 to Grd | 12v ± 1.5v | Switch in ON position – no voltage; possible defective switch. |
| Test Points | Spec | Comments |
| 544 to Grd | 12v ± 1.5v | Possible defective switch or open circuit. |
| 541 to Grd | 12v ± 1.5v | Switch held in set position – possible defective switch or open circuit. |
| 545 to Grd | 12v ± 1.5v | Switch held in resume position – possible defective switch or open circuit. |
Voltage circuit checks are performed at the ECM connector with the breakout box installed and the ignition key ON. The cruise switch circuit checks are listed in Table
“Cruise PTO ON/OFF Switch Circuit”
.
| Test Points | Spec | Comments |
| 35 to 42 | 12v ± 1.5v | Switch in ON position – no voltage, open circuit. |
| 35 to 42 | 0 | Switch in OFF position – voltage; short to power. |
The set switch circuit checks are listed in Table
“Set Switch Circuit”
.
| Test Points | Spec | Comments |
| 32 to 42 | 12v ± 1.5v | Switch held in SET position – no voltage, open circuit. |
| 32 to 42 | 0 | Switch in Middle position – voltage; short to power. |
The resume switch circuit checks are listed in Table
“Resume Switch Circuit”
.
| Test Points | Spec | Comments |
| 31 to 42 | 12v ± 1.5v | Switch held in RESUME position – no voltage, open circuit. |
| 31 to 42 | 0 | Switch in Middle position – voltage; short to power. |
Fault Code Descriptions
Flash Code 221 = SCCS or PTO switch signal, incorrect voltage signal; wrong for switch state.
Section 40.1.4
Cruise Control Description
Cruise control allows the ECM to control the engine’s power delivery to maintain a constant speed. The speed set point is determined by the driver. High and low set points are programmed into the ECM. These are the cruise high set limit and cruise low set limit. Also, the minimum engine speed at which the cruise control can be engaged, is programmed into the ECM.
Placing the cruise control ON/OFF switch in the on position supplies 12 volts to the ECM pin 35 to enable the cruise control. When the ON/OFF switch is in the ON position, it supplies the voltage for the Set/Resume switch. Depressing the Set switch will supply a 12 volt signal at the ECM pin 32 to reactivate the cruise set speed to the last active set speed. Or, if the cruise is active, depressing the resume (accel) switch will cause the set speed to increase.
Depressing the OFF switch, brake, clutch or placing the automatic transmission in neutral, will deactivate the cruise control. Cruise control will not be functional if the VSS signal is in fault.
Section 40.1.5
PTO (Engine Speed) Control
PTO speed control allows an operator to set a fixed engine speed, either in the cab, or remotely. In cab PTO uses the same switches on the dash as are used for the cruise control. Remote PTO uses switches that are installed by a body builder and are wired into the wiring harness of the vehicle at the body builder connections. There are two features that utilize the PTO speed controls — remote accelerator pedal and hydraulic pressure governing.
Section 40.1.6
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
Section 40.1.6.1
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 the two pre-programmed values for engine speed. To operate, turn the On/Off switch to the ON position. This sends a 12 volt signal to pin 35 of the ECM. The, depress either the Set or Resume switch. Depressing the Set switch sends a 12 volt signal to pin 32 of the ECM. This will cause the engine speed to run at the value programmed into PTO Set Speed.
Depressing the OFF switch, brake pedal, clutch pedal, or placing the automatic transmission in gear, as well as 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 or brake signal is in fault.
Section 40.1.6.2
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 driver to set the engine speed to a desired value. The control module will then maintain this speed over varying load conditions up to the rated power of the engine in the selected speed range.
To enable, turn the On/Off switch to the ON position. This sends a 12 volt signal to pin 35 of the ECM. Speed may be adjusted two ways. First the operator may adjust the engine speed with the accelerator and then depress the Set switch. This sends a 12 volt signal to pin 32 of the ECM. Or, the operator may depress the Resume/Accel switch, sending a 12 volt signal to pin 31 of the ECM to increase the speed incrementally. Also the operator may depress the Set/Coast switch to decrease engine speed.
Engine set speed will be limited to the value programmed in the ECM for maximum PTO speed.
Depressing the Off switch, brake pedal, clutch pedal, or placing the automatic transmission in gear, as well as 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 or Brake signal is at fault.
Section 40.1.6.3
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. Refer to In Cab Variable for more details. The maximum speed of the vehicle is programmable up to 20 mph. Disabling this mode is the same as In Cab Variable. A speed signal will not disable the speed control until the pre-programmed maximum speed is achieved.
Section 40.1.7
Remote PTO
Remote PTO can be enabled by two means. Operation of the speed control depends on which signal is enabled.
Section 40.1.7.1
Remote Preset
Enabling the remote preset signal allows for the engine to maintain a pre-programmed speed. When in the preset mode, a signal at the set terminal will cause the engine to run at the pre-programmed set speed. A signal at the resume terminal will allow the engine to run at the pre-programmed resume speed.
To operate, a 12 volt signal is sent to ECM pin 37. With the remote preset enabled, the speed is adjusted as with In Cab Preset.
Opening the switch to pin 37, or depressing the brake pedal, clutch pedal, or placing the automatic transmission in gear, as well as a signal from the VSS will deactivate the PTO speed control. However, the pre-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 or brake signal is in fault.
Section 40.1.7.2
Remote Variable
Enabling the remote variable signal allows for the engine speed to be adjusted to the desired level. A signal to the resume (accel) terminal will cause the engine speed to increase; a signal to the set (coast) terminal will cause the engine speed to decrease.
To operate, a 12 volt signal is sent to the ECM pin 36. With the remote variable enabled, the speed is adjusted as with In Cab Variable above. Refer to “40.1.6.2 In Cab Variable”
.
Opening the switch to pin 37 or depressing the brake pedal or clutch pedal or placing the automatic transmission in gear, as well as a signal from the VSS will deactivate the PTO speed control. However, the pre-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 or brake signal is in fault.
Section 40.1.8
PTO Speed Ramp Rate
The rate at which the speed of the engine will change will depend on load conditions and on a pre-programmed value called PTO speed ramp rate. A higher value will cause the engine to change speed more quickly.
Section 40.1.9
Fault Detection Management
The ECM monitors the signals for proper voltages and will set Flash Code 221. If the ignition switch is turned off, the fault will be recorded as an inactive fault.
Section 40.1.10
Flash Code 221
ATA Code SID 244 FMI 2
ECM: SCCS Switch or circuit fault.
The ECM monitors the cruise control and PTO inputs. If the expected value for each input does not match the expected status, a fault code is set.
Section 40.1.11
Troubleshooting
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 properly. Using the menu option of programmable parameters, the programming can be verified to ensure the ECM is programmed properly for the application. Also the data list can be used to monitor the parameters that cause the interruption of PTO speed control. Use the Diagnostic Code menu to read fault codes.
Section 40.1.12
Before Troubleshooting
Before troubleshooting, ensure the batteries are fully charged. Check battery connections and grounds for clean, tight connections, free of damage. Voltage test will give misleading results if the batteries are not fully charged.
Before troubleshooting, inspect circuit connectors for pushed back, loose or damaged (spread or bent) terminals, or wires with cut strands, etc. Wires and connections must be free of damage or corrosion. When some connectors corrode, a light white residue will be present and must be removed.
Before troubleshooting, inspect suspect circuit grounds for clean, tight connections, free of damage.
| Series 40E Troubleshooting Manual – 6SE241 |
| Generated on 10-13-2008 |