Cruise Control Description and Operation L81
Cruise control is a speed control system that maintains a desired vehicle speed
under normal driving conditions at speeds above 40 km/h (25 mph). Steep
grades may cause variations in the selected vehicle speeds.
The following are the main components of the cruise control system:
| • | The Resume/Accel switch |
| • | The engine control module (ECM) |
| • | The cruise brake switch |
| • | The throttle actuator control (TAC) motor |
| • | The vehicle speed sensor |
Cruise Control Engaged
The cruise control system will engage and adjust vehicle speeds, based on the
activation of the following cruise control switches:
The ECM monitors the signal circuits of the cruise control switches in order
to determine when to capture and maintain the selected vehicle speed. The ECM uses
the TAC motor in order control and maintain the vehicle speed. For further information
on the TAC system, refer to
Throttle Actuator Control (TAC) System Description
in Engine Controls - 3.0L (L81)
Ignition positive voltage is supplied from the 2-ampere CRUISE SWITCH fuse to
the cruise control switch via the ignition 3 voltage circuit. When the normally
open cruise control On/Off switch is turned On, the switch closes and the amber switch
indicator illuminates, and the ECM detects a high signal voltage on the cruise control
on switch signal circuit. When the normally open set/coast switch is pressed, the
switch closes and the ECM detects a high signal voltage on the cruise control set/coast
switch signal circuit. To engage the cruise control system, turn the On/Off switch
On and momentarily press the set/coast switch. The ECM will confirm that the cruise
control enable criteria has been achieved. The ECM will engage the cruise control
system and record the selected vehicle speed. The ECM sends a class 2 message
to the instrument panel cluster in order to illuminate the cruise control indicator.
Pressing the accelerator pedal, while the cruise control system is engaged, will allow
the driver to override the cruise control system in order to accelerate the vehicle
beyond the current set vehicle speed. When the accelerator pedal is released, the
vehicle will decelerate and resume the current set vehicle speed. The driver can also
override the current set vehicle speed via the set/coast switch and the resume/accel
switch. When the cruise control system is engaged, pressing and holding the set/coast
switch will allow the vehicle to decelerate from the current set vehicle speed without
deactivating the cruise control system. When the set/coast switch is released, the
ECM will record the vehicle speed and maintain the vehicle speed as the new set vehicle
speed. When the cruise control system is engaged, momentarily pressing the set/coast
switch will allow the vehicle to decelerate at 1.6 km/h (1 mph) increments
for each time that the set/coast is momentarily pressed, with a minimum vehicle speed
of 37 km/h (23 mph). When the normally open resume/accel switch is activated,
the switch closes and the ECM detects a high signal voltage on the cruise control
resume/accel switch signal circuit. Pressing and holding the resume/accel switch,
when the cruise control system is engaged, will allow the vehicle to accelerate to
a greater vehicle speed than the current set vehicle speed. When the resume/accel
switch is released, the ECM will record the vehicle speed and maintain the vehicle
speed as the new set vehicle speed. When the cruise control system is engaged, momentarily
pressing the resume/accel switch will allow the vehicle to accelerate at 1.6 km/h
(1 mph) increments for each time that the resume/accel switch is pressed, with
the maximum acceleration total of 16 km/h (10 mph) over the current
set vehicle speed. Momentarily pressing and releasing the resume/accel switch, after
the cruise control system has been disengaged by pressing the brake pedal, will recall
the previous set vehicle speed that is recorded in the ECM.
Cruise Control Disengaged
The ECM disengages the cruise control operation based on the signals from the
following switches:
| • | The cruise brake switch |
| • | The cruise control On/Off switch |
The cruise brake switch and the stop lamp switch are mounted on the brake pedal
bracket. When the brake pedal is applied, the normally closed cruise brake switch
opens and the normally open stop lamp switch closes. The ECM detects a low signal
voltage on the cruise control release signal circuit and a high signal voltage on
the stop lamp switch signal circuit. The vehicle speed stored in the memory of the
ECM will be erased when the cruise control On/Off button is turned OFF, or the ignition
switch is turned OFF.
The cruise control system will disengage when the ECM detects that a driver
override function has been active for approximately 60 seconds.
When the cruise control system is disengaged, the ECM sends a class 2
message to the instrument panel cluster (IPC) in order to deactivate the cruise indicator.
Cruise Control Inhibited
The ECM inhibits the cruise control operation when any of the following conditions
exist:
| • | The vehicle speed is less than 40.2 km/h (25 mph). |
| • | The vehicle is in PARK, REVERSE, NEUTRAL, or 1st gear. |
| • | The engine RPM is high, with fuel cut off. |
| • | The vehicle speed is too high, with fuel cut off. |
| • | The system voltage is not between 9 volts and 16 volts. |
| • | The antilock brake system/traction control system is active for more
than 2 seconds. |
