Cruise Control Description and Operation 8.1L

Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions. However, steep grades may cause variations in the selected speeds. The electronic cruise control system has the capability to CRUISE, COAST, RESUME SPEED, ACCELERATE, and TAP-UP or TAP-DOWN.

The main parts of the cruise control system are:

The cruise control system uses the TAC module to maintain the desired vehicle cruise speed and operation. The TAC and the powertrain control module (PCM) communicate together to vary the throttle opening in each different cruise control mode. The PCM monitors vehicle speed and operates the throttle actuator. The throttle actuator operates in response to the TAC module, to maintain the desired cruise speed. The throttle actuator motor moves the throttle blade. The PCM assembly contains a low speed limit which will prevent system engagement below a minimum speed of 40 km/h (25 mph). The TAC or PCM module assembly are not serviceable.

The operation of the TAC module is through the function control switches located on the multifunction turn signal lever. The cruise control function control switches includes the ON/OFF, SET/COAST, R/A (resume/accelerate). The switch assembly provides driver control of the cruise control system.

The stoplamp switch or CPP switch , is used to disengage the cruise control. A TCC/Brake signal circuit and a stoplamp switch signal circuit are used. The stoplamp and CPP switches are mounted to the brake pedal bracket and the stoplamp interface module is located near the TAC module behind the right side instrument panel. To disengage the system the driver presses the brake pedal or clutch pedal. The speed of the vehicle at brake actuation will be stored in the memory of the TAC module.

With cruise control, the vehicle can maintain a speed of about 40 km/h (25 mph) or more without keeping your foot on the accelerator. When the driver turns off the cruise control ON/OFF switch or ignition switch, the cruise control turns off. The vehicle speed stored in the memory of the TAC module will be lost.

Ignition positive voltage is supplied from the ETC fuse, to the TAC module. The TAC module is grounded to the chassis. When the cruise control ON/OFF switch is placed in the on position, ignition positive voltage is applied to the cruise control on switch signal circuit terminal of the TAC module. Cruise control is canceled when the driver presses either the brake pedal or clutch pedal. If the driver has not pressed the clutch pedal, ignition positive voltage is supplied through the CPP switch, to the CPP switch signal circuit terminal of the PCM. Ignition positive voltage is supplied to the stoplamp interface module from the ignition switch circuit breaker. The module is grounded to the chassis. When the driver presses the brake pedal, the stoplamp switch contacts of the stoplamp switch close applying ignition positive voltage to the stoplamp switch signal circuit of the stop lamp interface module. At the same time, the TCC/Brake switch contacts of the stoplamp switch open, removing the ground path to the brake switch signal circuit of the stoplamp interface module. The stoplamp interface module receives and interprets all stoplamp switch signals. The stoplamp interface module provides a brake pedal position (applied/released) through the signal circuits to the TAC module and PCM. When pressing the SET/COAST button on the multifunction turn signal lever, ignition positive voltage is applied to the set/coast switch signal circuit terminal of the TAC module. When pressing the R/A (resume/accelerate) on the control switch, ignition positive voltage is applied to the resume/accelerate switch signal terminal of the TAC module.

When the cruise switch is in the ON position, and the driver presses the SET/COAST button, the TAC module notifies the PCM that the cruise control is requested. The PCM then checks to see that the cruise control enable criteria is met. If the cruise control enable criteria has been met the PCM engages cruise control operation and controls the throttle opening.

The PCM will inhibit cruise control:

If the PCM determines that any of the cruise control inhibit conditions are present, the PCM will disengage the cruise control. The PCM accomplishes this through data communication with the TAC module. If the PCM disables the cruise control for an inhibiting event it will record the reason for disengagement in the Disengage Definition data file.