If the vehicle is equipped with RPO KSG, it also has Adaptive Cruise Control. Refer to the Object
Detection or the Driver Assistance Systems subsection for schematics, diagnostics, and
description and operation related to Adaptive Cruise Control functions.
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 accelerator pedal
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/accelerate switch)
The − SET switch (equivalent to set/coast switch)
The engine control module (ECM)
The throttle actuator control (TAC) motor (gasoline engines only)
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.
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.
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:
On/Off
+ RES
− SET
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.
Refer to the vehicle owner’s manual for the location and operation of the cruise control On/Off
indicators and driver information center (DIC) messages.
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 a vehicle
specific calibratable increment, commonly 1 km/h or 1 mph, each time that the − SET is
momentarily pressed, with a minimum vehicle speed of 38 km/h (24 mph). Refer to the vehicle
Owner’s Manual for more information.
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 a vehicle specific calibratable increment,
commonly 1 km/h or 1 mph, each time that the + RES switch is momentarily pressed. Momentarily
activating the + RES switch will recall the previous vehicle speed, after the cruise control system
has been disengaged by pressing the brake pedal, or CANCEL switch. Refer to the vehicle Owner’s
Manual for more information.
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 On/Off switch
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 is further applied. The ECM monitors the BPP signal through a discrete
input and a serial data message signal from the BCM indicating the brake status. When either
signal indicates 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. 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 the Cruise Control System
is active and disengagement is requested.
When engagement of the system is requested but an engagement inhibit is present, the most
recent inhibit reason is recorded in the ECM history. The scan tool will display the most recent
inhibit reason, in which one out of approximately 50 possible reasons will be displayed.
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) this
ignition cycle.
A Cruise Control System DTC has been set.
The vehicle speed is less than 38.6 km/h (24 mph).
The vehicle speed is too high.
The vehicle is in PARK, REVERSE, NEUTRAL, or 1st gear.
The engine RPM is low.
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 a
calibratable time (typically 0.3 to 0.7 seconds).
Cruise Control Inhibit Reasons
This is a general list of inhibit reasons. Not every inhibit reason is applicable to all vehicles. Refer
to the scan tool inhibit reason list for the last 8 reasons that have been recorded during the
current ignition cycle.