Cruise Control: Description and Operation

DESCRIPTION
The speed control system is electrically controlled and vacuum operated. The control lever on the steering column incorporates a slide switch which has three positions: Off/On, Resume/Accel and Set/Decel. The Set button is located at the end of the three position slide switch. The system is designed to operate at speeds exceeding 35 MPH.

OPERATION
The engine controller monitors critical input and output circuits within the speed control system, making sure they are operating correctly. If a problem is sensed by the controller often enough to be considered a malfunction, it is stored in the controller memory in the form of a diagnostic trouble code message. These messages are short descriptions of a defective condition that exists or of a certain circuit experiencing a malfunction. If the problem is repaired or ceases to occur, the controller will cancel the message after 50 ignition key On/Off cycles.

To engage the speed control when desired speed is achieved, depress and release the Set button to engage the system. Speed will be maintained at this level. Moving the slide switch from Off to On position while vehicle is in motion establishes memory without system engagement.

To disengage speed control, a normal brake application or soft tap on the brake pedal will disengage system without erasing speed memory. Moving the slide switch to Off position also disengages the system, but will erase the speed memory.

CIRCUIT OPERATION
The Powertrain Control Module (PCM) operates the vehicle speed control system. The vehicle speed control switches are located in the steering wheel.

Circuit V32 from cavity C11 of the PCM connects to circuit V30 through the stop lamp switch. Circuit V30 powers the vehicle speed control servo.

Circuit K95 from PCM cavity C32 connects to the vehicle speed control switches. The switches are wired in parallel and each contains a separate resistor. The voltage level present on circuit K95 (at PCM cavity C32) depends on which speed control switch is selected. Circuit K4 from PCM cavity A4 supplies ground for the speed control switches.
- When the ON/OFF switch is open, the voltage level on circuit K95 at PCM cavity C32 has a nominal value of 5.0 Volts with a range from 4.8 to 5.0 Volts.
- When the ON/OFF switch closes, the voltage level on circuit K95 at PCM cavity C32 has nominal value of 1.51 Volts with a range from 1.31 to 1.61 Volts.
- When the SET switch closes, the voltage level on circuit K95 at PCM cavity C32 has nominal value of 3.8 Volts with a range from 3.6 to 3.9 Volts.
- When the RESUME/ACCEL switch closes, the voltage level on circuit K95 at PCM cavity C32 has nominal value of 4.4 Volts with a range from 4.2 to 4.5 Volts.
- When the COAST switch closes, the voltage level on circuit K95 at PCM cavity C32 has nominal value of 2.92 Volts with a range from 2.72 to 3.02 Volts.
- When the CANCEL switch closes, the voltage level on circuit K95 at PCM cavity C32 has is 0.1 Volts or less.

The PCM controls the vent and vacuum functions of the vehicle speed control servo on circuits V35 and V36. Depending on the signal it receives from vehicle speed control switches, the PCM either applies vacuum to or vents vacuum from the servo. Circuit V36 from cavity C4 of the PCM sends the vacuum signal to the servo. Circuit V35 from cavity C5 sends the vent signal.

Circuit L53 provides the stop lamp switch sense input to the PCM at cavity C24. The stop lamp switch connects circuit L53 to ground on circuit Z1. When the brake pedal is depressed, the stop lamp switch opens and disconnects circuits L53 and Z1, and circuits V32 and V30. When the stop lamp switch disconnects circuits V32 and V30, power is removed from the speed control servo.