Cruise Control Switch

Cruise control system is electrically actuated and vacuum operated. Cruise control switch controls are located on steering wheel. When speed control is selected by depressing the ON/OFF switch, the PCM allows a set speed to be stored in its RAM for speed control. To store a set speed, depress the SET switch while the vehicle is moving at a speed between about 35-85 MPH. In order for the speed control to engage, the brakes cannot be applied and the gear selector cannot indicate the transmission is in Park or Neutral. If the driver wishes to increase vehicle speed while the speed control is engaged, the PCM is programmed for an acceleration feature. With the ACCEL switch held closed, the vehicle accelerates slowly to the desired speed. The new target speed is stored in the PCM's RAM when the ACCEL switch is released. The PCM also has a "tap-up" feature in which vehicle speed increases at a rate of about 2 mph for each momentary switch activation of the ACCEL switch. The PCM also provides a means to decelerate without disengaging speed control. To decelerate from an existing recorded target speed, depress and hold the COAST switch until the desired speed is reached. Then release the switch. The ON/OFF switch operates two components, the PCM's ON/OFF input, and the battery voltage to the brake switch, which powers the speed control servo.

The cruise control switches are on a single circuit. The PCM sends out 5 volts through a fixed resistor and monitors the voltage change between the fixed resistor and the switches. If none of the switches are depressed, the PCM will measure 5 volts at the sensor point (open circuit). If a switch with no resistor is closed, the PCM will measure 0 volts (grounded circuit). If a resistor is added to a switch, then the PCM will measure some voltage proportional to the size of the resistor. By adding a different resistor to each switch, the PCM will see a different voltage depending on which switch is pushed. Another resistor has been added to the "at rest circuit" causing the PCM to never see 5 volts. This was done for diagnostic purposes. If the switch circuit should open (bad connection), then the PCM will see the 5 volts and know the circuit is bad. The PCM will then set an open circuit fault. For additional information and diagnostic testing, see appropriate CRUISE CONTROL article in ACCESSORIES & EQUIPMENT.