System Operation

Speed control system operates when vehicle speed is 35-85 MPH, vehicle is in gear, and clutch and brake are released. When conditions are met, PCM controls solenoid valve body to apply and release vacuum from vacuum reservoir to vacuum servo. Vacuum is stored in vacuum reservoir, located behind front bumper (Cherokee) or on right inner front fender (Wrangler). The vacuum servo contains a diaphragm connected to throttle linkage. Using input from Vehicle Speed Sensor (VSS), PCM adjusts vehicle speed. The vacuum and vent solenoids are supplied duty cycled ground by PCM to control vacuum to servo. The brake light switch supplies power to dump solenoid and solenoid valve body when released. When brake pedal is applied, power is disconnected. The dump valve opens, releasing vacuum from servo.

Speed control can be manually disengaged by stepping on the brake pedal, pressing OFF switch, pressing CANCEL switch or by depressing clutch pedal. Speed control system will automatically disengage if Park or Neutral signal is sent from TCM, if engine RPM increases rapidly (as when clutch is pressed), if VSS signal increases at a rate of 10 MPH per second (as in tires losing traction) and if VSS signal decreases at a rate of 10 MPH per second (as in vehicle rapidly decelerating).