Circuit Operation

The Cruise Control Module contains a stepper motor which positions a cable connected to the throttle. The Cruise Control cable operates the throttle in the same manner that the accelerator cable does. The Cruise Control cable is wound on a reel in the module and the stepper-motor turns the reel in one direction or another to control the position of the throttle and thus control vehicle speed. When the Cruise Control system is idle or disabled, the stepper motor is disengaged and the cruise control cable is free to move in accordance with motion of the accelerator cable. When Cruise Control is set or engaged, the stepper motor will engage the cable and position the cable to maintain a minimum speed. Use of the accelerator to increase speed is permitted, but release of the accelerator will not decrease speed to less than set by the Cruise Control module. Also, the Cruise Control system will not limit speed when the vehicle coasts down a hill.

The Cruise Control Module is powered with the Ignition Switch in RUN by CRUISE Fuse 6 through the BRN (41) wire. This fuse also provides operating voltage for the Cruise Control Switch located on the Steering Column in the Multi-Function Lever. The Cruise Control Module is grounded by the BLK/WHT (451) wire at Ground G103.

The Cruise Control Switch consists of two switches and provides three separate inputs to the Cruise Control Module. The Cruise Control Switch consists of a SET CRUISE pushbutton and a three position OFF-ON-R/A slider switch. With the three-position OFF-ON-R/A slider switch in the center ON position, the ON input is delivered by the GRY (387) wire to the Cruise Control Module. This input enables Cruise Control Module response to the other two switch inputs. Placing the Cruise Control Switch's OFF-ON-R/A slider switch in the OFF position while Cruise Control is engaged will disengage the Cruise Control System without retaining speed setpoint memory.

The SET CRUISE pushbutton input is delivered by the DK BLU (84) wire. The pushbutton input must he present in order to initially engage Cruise Control. With Cruise Control not yet engaged, this pushbutton input sets the speed at which the Cruise Control Module will operate until otherwise directed. Once Cruise Control is initially engaged, this same "set" input can be used for two other functions. If the SET CRUISE pushbutton is depressed for a short time (less than second), the input will cause the Cruise Control Module to Tap-Down the speed setpoint by 1.6 KPH (1 mph). Repeated Tap-Down operations can be performed as long as the vehicle speed remains above the lower limit for Cruise Control operation. Cruise Control will not engage with vehicle speeds lower than 40 KPH (25 mph) approximately. If the pushbutton is depressed for a longer period of time, the Cruise Control Module will disengage the throttle and wait for the pushbutton to be released and the vehicle will coast. When the pushbutton is released, the Cruise Control Module will reengage with the current speed as the control setpoint.

The R/A (Resume/Accelerate) input is provided on the GRY/BLK (87) wire. The OFF-ON-R/A slider switch R/A position is a momentary contact switch like a pushbutton. This switch input also has three functions. If Cruise Control was operating and then disengaged by actuation of the Brake Pedal, then this input will cause the Cruise Control Module to "resume" operations at the previously set speed setpoint. If the engine has been turned off or the Cruise Control Switch has been placed in OFF since the previous operation, no response will occur.

With Cruise Control already engaged, an R/A input will tend to cause the vehicle to accelerate. If the switch is depressed for a short time (less than a second), the Cruise Control Module will Tap-Up speed by 1.6 KPH (1 mph). The Tap-Up operation may be repeated. If the switch is actuated for a longer period of time, the Cruise Control Module will increase vehicle speed (Accelerate) over time until the switch is released. When the switch is released, the current speed becomes the new speed setpoint. Accelerating with the Cruise Control Switch while the vehicle operates under heavy load or prolonged accelerating with the Cruise Control Switch may cause the automatic transmission to downshift. As with the use of the accelerator, engine damage may occur if the engine speed becomes excessive.

The Cruise Control Module monitors two TCC/Stoplamp Switch inputs. Voltage is supplied to TCC/Stoplamp Switch Pin "D" from BRAKE Fuse 18 (Hot in RUN). The TCC/Stoplamp Switch sends an enable signal from Pin 'C" to the Cruise Control Module over the PPL(420) wire. With the brake released, this signal is present and Cruise Control operations may be engaged. The loss of this voltage, as when the Brake Pedal is depressed, will cause the Cruise Control Module to disengage. The Cruise Control Module retains previous speed setpoint information in case operations are resumed. Intermittent opens or shorts to ground on the PPL(420) wire will also cause Cruise Control to disengage.

The other TCC/Stoplamp Switch input on the WHT (17) wire is used to check TCC/Stoplamp Switch operation before engaging Cruise Control. Power to TCC/Stoplamp Switch Pin 'E" is available at all times through the ORN (140) wire. After the Ignition Switch is placed in RUN, the brake must be depressed to provide the Brake Before Cruise input through the WHT (17) wire. After TCC/Stoplamp Switch operations are confirmed, then the Cruise Control Module will respond to a SET input.

The Cruise Control Module monitors a vehicle speed signal from the Vehicle Control Module (VCM) on the DK GRN/WHT (817) wire. This 4000 pulses per mile input is used for setting and for controlling vehicle speed. This input will generate an RMS voltage of between zero to five volts depending upon speed when measured with a high input impedance voltmeter.

The Cruise Control Module signals the Vehicle Control Module (VCM) that Cruise Control is engaged on the LT BLU/BLK (396) wire. The Vehicle Control Module (VCM) may use this information in control of transmission
shifting. If a new VCM is installed, it must be told that the Cruise Control Module is present by engaging, disengaging, and reengaging Cruise Control. (Refer to Engine Controls section for the specific engine). Computers and Control Systems