Q: How Does the Cruise Control System and Cruise Control Module Work on Honda Prelude?
A: The cruise control system is a vacuum-based system designed to work at speeds above 25mph. To activate it, the cruise control dash mounted main switch must be in the on position, which can be toggled on and off by pressing it. When on, an indicator light in the switch will light up. The system works a mechanical linkage to the throttle via a vacuum motor inside a server, a diaphragm moved by vacuum applied to one side. A solenoid driven valve connects the vacuum motor to a vacuum tank, while another solenoid vents the vacuum. The cruise control module controls the servo and the throttle by pulsing these solenoid valves on and off. One input to the cruise control module is the vehicle speed, sent to the Powertrain Control Module (PCM) by the Vehicle Speed Sensor(VSS). To diagnose the system, first note the symptom. If the system does not engage at all, check the main switch, brake and clutch (if installed) pedal adjustments, wiring for the cruise vacuum unit and control unit, vacuum hose connections for the vacuum unit, vacuum unit throttle cable, and speedometer operation. If the system loses speed, check the vacuum hoses for the vacuum unit for leaks and the vacuum storage tank for leaks. If the vehicle loses speed before the system engages, check the cable adjustment from the vacuum unit to the throttle for excessive free play.