Cruise Control: Description and Operation

THEORY OF OPERATION:
When the "SET" switch is pressed the vehicle must be moving forward at a speed between 35 and 85 mph, with the transmission gear selector in other than park or neutral. The PCM locks in a set speed. Then the PCM energizes the vacuum and vent solenoid to open the throttle and deactivates the vent solenoid to close the throttle. These actuations are dependent on power supplied to the servo from either the speed control relay or the PCM. The system is deactivated by pressing the brake, turning the on/off switch to OFF, or vehicle speed falling below the minimum. Reactivation can be done by repeating the previous steps or pressing resume with the vehicle speed between 35 and 85 mph.

CIRCUIT OPERATION:
The vehicle speed control system is powered by the Powertrain Control Module (PCM). The vehicle speed control switches, located in the steering wheel, use resistors internal to the switch to send a signal to the PCM indicating what the operator is requesting. The V37 circuit, from cavity 41 of the PCM, supplies power for the switch. Circuit Z2 is the ground for the switch.

The V37 and Z2 circuits are spliced internal to the clockspring to provide power and ground for the switches.

When the system is turned ON, the vehicle is moving forward, vehicle speed is above 35 mph, and the SET switch is pressed, the PCM looks at the vehicle speed through the vehicle speed sensor on the manual transmission equipped vehicles. On vehicles equipped with the automatic transmission, the vehicle speed input is provided from the Transmission Control Module (TCM) to the PCM.

With this information, the PCM sends a signal to the vehicle speed control servo, on the V36 circuit, and the servo applies vacuum to hold the desired speed. Circuit V36 connects to cavity 78 of the PCM.

When the operator selects the COAST feature in the system, the PCM measures the resistance on the V37 circuit and uses this information to apply voltage on the V35 circuit, which is the vent side of the vehicle speed control servo. Circuit V35 connects to cavity 80 of the PCM.

Grounding for the vehicle speed control servo is supplied on the Z1 circuit. Circuit Z1 terminates at the left strut tower. An additional input to the servo is provided by the stop lamp switch on the V30 circuit. When the operator presses on the brakes the ground path for the V30 circuit is broken. This break in the ground path causes the vehicle speed control servo to vent and disengage the system.

Circuits V32 and K29 are used as inputs to the PCM to indicate when the operator is applying the brakes, as vehicle speed control is canceled when this happens. Circuit V32 connects to cavity 5 of the PCM. Circuit K29 connects to cavity 62 of the PCM.