Circuit Operation

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

Circuit V32 from cavity C11 of the PCM supplies 12 volts to the Light Emitting Diode (LED) used for the speed control indicator lamp. Circuit V32 also connects to circuit V30 through the stop lamp switch. Circuit V30 powers the vehicle speed control servo.

Circuit V33 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 V33 (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 V33 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 V33 at PCM cavity C32 has nominal value of 1.51 volts with a range from 1.31 to 1.61 volts.
- When the SET/COAST switch closes, the voltage level on circuit V33 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 V33 at PCM cavity C32 has nominal value of 4.4 volts with a range from 4.2 to 4.5 volts.

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 K29 provides the stop lamp switch sense input to the PCM at cavity C24. The stop lamp switch connects circuit K29 to ground on circuit Z1. When the brake pedal is depressed, the stop lamp switch opens and disconnects circuits K29 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.