Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide



See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Cruise control component diagram

The cruise control automatically controls the vehicle speed and allows the vehicle to run at a constant speed without depressing the accelerator pedal. In operation, when the driver sets a desired speed with the cruise control switch, the built-in micro-computer compares the speed set in the memory with the actual running speed detected by feedback signals from the speedometer. This feedback system operates the throttle of the carburetor or throttle body to correct the speed difference, thereby keeping the vehicle at a constant speed. The major components are the main switch, cruise switch, control unit, vacuum pump and valve assembly, actuator, clutch switch and stop and brake switch.

The use of the speed control is not recommended when driving conditions do not permit maintaining a constant speed, such as in heavy traffic or on roads that are winding, icy, snow covered or slippery.


Cruise control unit compares the actual vehicle speed detected by feedback signals from the speed sensor incorporated in the speedometer with the speed set in the memory memorized when the set switch was turned ON . A signal is then transmitted according to the difference between the 2 speeds.

This signal is transmitted to the solenoid valves of the valve assembly located in the engine compartment. The movement of the actuator operates the throttle valve through the accelerator pedal and cable, thereby keeping the vehicle's speed constant.


Vacuum Pump

The vacuum pump is controlled by the vacuum switch built into the valve assembly tank, and is used to supply the vacuum to the tank. Power to the pump is fed when the vacuum switch is turned ON , and the diaphragm is moved up and down by the rotation of the offset shaft fixed to the motor shaft.

Vacuum Valve Assembly

The vacuum valve, vent valve, and safety valve provide the open-close operation which leads to the vacuum/atmospheric pressure to the actuator. Also attached to this assembly is the tank for storing vacuum generated by the pump, and the vacuum switch for controlling the pump to maintain a constant vacuum level in the tank.

If the cruise control is turned ON and a constant vehicle speed is attained, the safety valve connected to the atmosphere is closed. Also, the vacuum valve connected to the tank and the vent valve connected to the atmosphere operate to lead the atmosphere/vacuum to the actuator. When the cruise control is canceled, the vacuum valve closes to shut off the tank vacuum, and the safety valve opens to allow atmospheric pressure to enter the actuator.

The vacuum in the tank is consumed by the operation of the vacuum valve. If the vacuum in the tank reaches 13 in. Hg (43 kPa) the vacuum switch is turned ON , and the pump feeds the vacuum into the tank. When the vacuum in the tank reaches 15 in. Hg (52 kPa) the vacuum switch turns OFF to stop the pump.


The diaphragm is operated by vacuum or atmospheric pressure led by each valve, and this diaphragm movement actuates the wire cable through the link assembly to open or close the throttle valve. With the cruise control set to OFF (system OFF state), no diaphragm operation occurs as the atmospheric pressure is kept inside the actuator.

Engine Throttle

The throttle body or carburetor is equipped with 2 throttle cams. One cam is used during acceleration and the other during cruising, in order to open or close the throttle valve. These cams operate independently of each other. In other words, while 1 cam operates, the other does not.


Properly disarm the air bag on vehicles equipped with the SRS system. Failure to do so can cause serious injury and/or damage.

Never disconnect any electrical connection with the ignition switch ON unless instructed to do so in a test.
Always wear a grounded wrist static strap when servicing any control module or component labeled with a Electrostatic Discharge (ESD) sensitive device symbol.
Avoid touching module connector pins.
Leave new components and modules in the shipping package until ready to install them.
Always touch a vehicle ground after sliding across a vehicle seat or walking across vinyl or carpeted floors to avoid static charge damage.
Never allow welding cables to lie on, near or across any vehicle electrical wiring.
Do not allow extension cords for power tools or drop lights to lie on, near or across any vehicle electrical wiring.
Do not operate the cruise control or the engine with the drive wheels off the ground unless specifically instructed to do so by a test procedure.