Cruise Control: Description and Operation

This vehicle does not use a Speed Control Amplifier. Instead, all Speed Control functions are handled by the Electronic Engine Control (EEC) Module.

When activated, the Speed Control System maintains vehicle road speed at a driver-selected rate. Using input information from the Vehicle Speed Sensor (VSS) and the Throttle Position Sensor, the EEC Module operates the Speed Control Servo Vacuum and Vent Valves to control the level of vacuum applied to the Speed Control Servo Motor. The Servo Motor, in turn, operates the engine throttle linkage through the Actuator Cable to speed up or slow down the vehicle.

Voltage is present at the Speed Control Switch Assembly ON contact at all times through Circuit Breaker 12, the Horn Relay coil and the Clockspring Assembly.

With the Ignition Switch in START or RUN, voltage is present at pins 37 and 57 of the EEC Module through circuit 361 (R).

EEC MODULE INPUTS

Backup Lamp/Neutral Safety Switch

With the gear selector in OVERDRIVE or DRIVE, pin 30 of the EEC Module is not grounded and the Speed Control System will operate. Moving the gear selector into NEUTRAL grounds pin 30 through the Backup Lamp/Neutral Safety Switch and the Starter Relay coil. This input causes the EEC Module to disengage Speed Control.

Speed Control Switch Assembly

The Speed Control Switch Assembly signals the EEC Module to turn the system on and off, to set and hod the vehicle speed, to resume and to accelerate or coast. With the Switch held ON, voltage is applied to pin 50 of the EEC Module. In OFF, pin 50 is grounded. With the Switch held in SET/ACCEL, 680 ohm resistor is placed in the ground circuit. In RESUME, a 2200 ohm resistor is placed in the ground circuit; in COAST, a 120 ohm resistor is used.

Stop Lamp Switch

With the brake pedal depressed, the Stop Lamp Switch contacts close, applying voltage to pin 2 of the EEC Module. This input causes the EEC Module to disengage Speed Control.

Throttle Position Sensor

The Throttle Position Sensor is a potentiometer connected to the throttle linkage. The EEC Module applies a reference voltage to the Sensor and monitors the return signal voltage. The feedback circuit provides information about throttle linkage position.

Vehicle Speed Sensor (VSS)

The Vehicle Speed Sensor (VSS) is a small, permanent magnet generator driven by a transaxle gear. Sensor output is proportional to vehicle road speed. With Sensor output indicating that vehicle road speed is above 30 mph, the EEC Module enables the Speed Control System. The Vehicle Speed Sensor (VSS) signal is used to maintain vehicle speed when the System is operating.

OTHER SYSTEM INPUTS

Vacuum Dump Valve

The Vacuum Dump Valve provides a mechanical means of disengaging the Speed Control System. With the brake pedal released, the Valve is closed, and the vacuum level in the System is determined by the Speed Control Servo Vacuum and Vent Valves. With the brake pedal depressed, the Dump Valve opens, disabling the vacuum circuit.

EEC MODULE OUTPUTS

Speed Control Servo

With the Speed Control System turned on and vehicle road speed above 30 mph, the EEC Module energizes the Vacuum and Vent Valves in the Speed Control Servo. The Vacuum and Vent Valves control the level of vacuum applied to the Servo Motor.