Cruise Control Servo

Servo consists of a vacuum-operated diaphragm, a normally open vent solenoid valve to vent diaphragm chamber to atmosphere, a normally closed vacuum solenoid valve to connect diaphragm chamber to vacuum source and a variable inductance position sensor. Servo operates throttle in response to signals from PCM as follows:

Steady Cruise State

Both vacuum and vent valves closed. Servo has constant vacuum pressure on diaphragm. Vacuum is trapped in diaphragm chamber.

Vehicle Speed Less Than Set Speed

Control module energizes vacuum solenoid to open vacuum valve to vacuum source. This increases vacuum level in servo to increase throttle opening. Vent remains closed.

Vehicle Speed Greater Than Set Speed

Control module de-energizes vent solenoid to open vent valve to atmosphere. This reduces vacuum to servo and allows throttle return spring to decrease throttle opening. Vacuum valve remains closed.