Cruise Control Description and Operation (Conventional Cruise
Control)
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 brake pedal position (BPP)
sensor |
• |
The body control module
(BCM) |
• |
The cruise on/off
switch |
• |
The cruise control cancel
switch |
• |
The + RES switch (equivalent
to resume/accel switch) |
• |
The - SET switch (equivalent
to set/coast switch) |
• |
The engine control module
(ECM) |
• |
The throttle actuator control
(TAC) motor |
• |
The vehicle speed
sensor |
The body control module (BCM) monitors the signal circuit of the
cruise control switches, which are located on the steering wheel.
The BCM relays the cruise control switch status to the engine
control module (ECM) via the serial data circuit. The ECM uses the
status of the cruise control switch to determine when to capture
and maintain the vehicle speed. The ECM monitors the vehicle speed
signal circuit in order to determine the desired vehicle speed. The
ECM uses the TAC motor in order to maintain the vehicle speed.
Voltage is supplied to the cruise control switch via the
steering wheel control switch reference voltage circuit supplied by
the BCM. The cruise control function switches are arranged in a
resistive ladder design, with each cruise control function switch
having a different resistance value. The BCM detects a specific
voltage value that is associated with the cruise control function
switch being activated. The BCM sends a serial data message to the
ECM indicating that the on/off switch is active. Similarly, when
the normally open + RES switch or the normally open - SET switch
are pressed, the switch closes and the BCM detects the
predetermined voltage signal on the cruise control resume/accel and
set/coast switch signal circuit. The BCM sends a serial data
message to the ECM indicating that the + RES switch or the - SET
switch is active. The + RES switch or the - SET switch will remain
inactive when the BCM has not received the predetermined voltage
signal from the on/off switch.
Cruise Control Engaged
The Cruise Control System will engage and adjust vehicle speeds,
based on the activation of the following cruise control switches,
which are located on the steering wheel:
To engage the Cruise Control System, ensure that the vehicle
speed is above 40.2 km/h (25 mph), turn the cruise On/Off switch ON
and momentarily press the - SET switch. The ECM will engage the
Cruise Control System and record the vehicle speed. The ECM sends a
serial data message to the instrument panel cluster (IPC) in order
to illuminate the Cruise Engaged indicator in the IPC.
Pressing the accelerator pedal while the Cruise Control System
is engaged, allows 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 switch
and the + RES switch. When the Cruise Control System is engaged,
pressing and holding the - SET switch will allow the vehicle to
decelerate from the current set vehicle speed without deactivating
the Cruise Control System. When the - SET 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 switch will allow the
vehicle to decelerate at 1.6 km/h (1 mph) increments for each time
that the - SET is momentarily pressed, with a minimum vehicle speed
of 37 km/h (23 mph).
Pressing and holding the + RES 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
+ RES 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 + RES
switch will allow the vehicle to accelerate at 1.6 km/h (1 mph)
increments for each time that the + RES switch is momentarily
pressed, with the maximum acceleration total of 16 km/h (10 mph)
over the current set vehicle speed. Momentarily activating the +
RES switch will recall the previous vehicle speed, after the cruise
control system is disengaged by pressing the brake pedal, or CANCEL
switch.
Cruise Control Disengaged
The engine control module (ECM) disengages the cruise control
operation based on the signals from the following switches:
• |
The brake pedal position (BPP)
sensor |
• |
The cruise control cancel
switch |
The Cruise Control System will disengage when the brake pedal is
applied. The body control module (BCM) monitors the BPP sensor via
the BPP sensor signal circuit as the voltage signal increases while
the pedal reaches the fully applied position. The ECM monitors the
BPP signal through a discrete input and a serial data message
signal from the BCM indicating the brake status. When both signals
indicate the brake pedal is applied, the ECM will disengage the
cruise control system.
The Cruise Control System will also disengage when the cruise
control on/off switch is switched OFF, or the cruise control cancel
switch is activated. The body control module (BCM) determines when
the cruise control cancel switch is activated. When the normally
open cancel switch is closed, the BCM detects the predetermined
voltage signal on the cruise control function switch circuit. The
vehicle speed stored in the memory of the engine control module
will be erased when the cruise control On/Off switch is turned OFF,
or the ignition switch is turned OFF. The BCM sends a serial data
message to the ECM in order to disengage the cruise control system.
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 has been disengaged, the
ECM sends a serial message to the instrument panel cluster (IPC) in
order to turn OFF the Cruise Engaged indicator.
Every time the Cruise Control System is disengaged, the ECM will
keep track of the reason for system disengagement. The last 8
disengagement reasons will be recorded within the ECM memory. The
scan tool will display the last 8 Cruise Disengage History
parameters, in which one out of approximately 50 possible reasons
will be displayed in each of these 8 parameters. For the
disengagement reason to be displayed within the scan tool parameter
either the Cruise Control System is active and disengagement is
requested, or engagement of the system is requested but a fault is
present.
Cruise Control Inhibited
The engine control module (ECM) inhibits the cruise control
operation when any of the following conditions exist:
• |
The ECM has not detected a
brake pedal activation from the body control module (BCM).
|
• |
A Cruise Control System DTC
has been set. |
• |
The vehicle speed is less than
40.2 km/h (25 mph). |
• |
The vehicle speed is too
high. |
• |
The vehicle is in PARK,
REVERSE, NEUTRAL, or 1st gear. |
• |
The engine RPM is high.
|
• |
The system voltage is not
between 9 volts and 16 volts. |
• |
The Antilock Brake System
(ABS)/Traction Control System (TCS) is active for more than 2
seconds. |
|