Cruise Control: Description and Operation
DESCRIPTIONThe 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 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 tbe switches.
On vehicles equipped with an electronically controlled transaxle, 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 input provided from the Transmission Control Module (TCM) to the PCM on circuit G7. On vehicles equipped not equipped with an electronically controlled transaxle, the PCM receives the vehicle speed input from the vehicle speed sensor.
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 done on the Z1 circuit. 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.