Cruise Control Description and Operation Adaptive Cruise

Adaptive Cruise Control (ACC)

The Adaptive Cruise Control (ACC) System is an enhanced cruise control system with the ability to sense and react to forward traffic. Compared to the common cruise control system found on many vehicles, the main functional enhancement of the ACC system is the ability to detect the presence of a vehicle in the path of the ACC vehicle. The ACC retains the existing cruise control feature that controls the vehicle speed to the driver selected speed. However, ACC allows a driver to set and maintain a following distance to the preceding nearest vehicle in the ACC vehicle path. The distance sensing cruise control module (DSCC) calculates a follow speed limit to ensure an acceptable distance is maintained to the preceding vehicle in front, should one be present. The ACC system automatically adjusts the speed of an ACC vehicle when the vehicle comes up behind a slower travelling vehicle in front. The ACC system applies limited automatic braking and throttle control without driver input when necessary to maintain the set following distance of the ACC vehicle. The preceding vehicles speed and acceleration along with the ACC vehicle speed and acceleration and the distance between the 2 vehicles are factors used by the DSCC to determine the ACC follow speed limit. The ACC vehicle speeds up to the original driver selected set speed when the pathway becomes clear without driver input.

Adaptive Cruise Control (ACC) System Description

The Adaptive Cruise Control (ACC) System depends on various modules on the vehicle to function and each module performs a function that is critical to the proper operation of the ACC System. ACC will not operate if any components fail. Communication between modules is via the high-speed General Motors local area network (GMLAN) and the class 2 serial data circuit. The body control module (BCM) provides a translating gateway function between the class 2 and the GMLAN data links. The GMLAN utilizes the controller area network (CAN) communications protocol. The following is a functional description of the distance sensing cruise control module (DSCC) and the other associated components:

Distance Sensing Cruise Control Module (DSCC)

The distance sensing cruise control module (DSCC) communicates with the forward looking sensor (FLS) via controller area network (CAN) serial data. The DSCC utilizes the FLS to identify and classify objects in the road environment. The FLS scans the road environment to detect targets within its specified field of view. The DSCC then makes throttle and/or brake commands to the engine control module (ECM) and electronic brake control module (EBCM) via GMLAN serial data circuit to control vehicle acceleration/deceleration based on data from the FLS radar. The ECM and EBCM provide throttle control and automatic braking needed for proper cruise speed adjustment. An internal yaw rate sensor is used by the DSCC to determine the predicted path of the adaptive cruise control (ACC) vehicle. The main power feed for the DSCC is the battery and this signal is always at battery potential. However, the ACC system only activates when the ignition 1 input is active and in the RUN position. The ignition 1 voltage signal to the DSCC has to be 9.2 volts or more to be considered active. When the ignition 1 signal is not active, all ACC functions are disabled. The following is a list of the DSCC functions:

Body Control Module (BCM)

The following are the ACC system functions provided by the BCM:

Engine Control Module (ECM)

The following are the ACC system functions performed by the ECM:

Electronic Brake Control Module (EBCM)

The following are the ACC system functions performed by the EBCM:

Refer to ABS Description and Operation.

Transmission Control Module (TCM)

The transmission control module (TCM) provides a down shift to protect the brakes. When the TCM detects some driver braking activity or ACC automatic braking activity, the TCM down shifts the vehicle transmission to increase engine braking. This helps reduce the ABS braking activity, extend brake pad life and reduce brake overheating.

Driver Information Center (DIC)

The DIC is a part of the instrument panel cluster (IPC) and displays the ACC system warning messages. The DSCC requests messages to be displayed on the DIC by sending a GMLAN request to the BCM. The BCM sends a class 2 serial data request to the DIC demanding the display of the warning message. When the message is acknowledged by the driver and the cause of the message resolved, the DIC turns the message off. These displays are accompanied by a chime warning internal to the DIC. The ACC system will not operate if the DIC fails. The following are the 3 ACC messages that can be displayed on the DIC:

Head-Up Display (HUD)

The head-up display (HUD) displays ACC system telltales and status information. The DSCC sends a message to the BCM via the GMLAN serial data circuit requesting the display of a HUD telltale. The HUD displays the telltale when it receives a class 2 message from the BCM demanding illumination of the telltale. Feedback to a driver action takes precedence over other status information sent to the HUD by the BCM. The HUD is enabled in power mode RUN. The driver may have to adjust the position of the HUD or the intensity of the display to see the information being displayed. The ACC system will not operate if the HUD fails. The HUD displays the following telltales and ACC status indicators:

Radio Amplifier

The amplifier receives audible warning commands via a class 2 message from the BCM. The chime alerts the vehicle driver to certain ACC vehicle conditions. The audible chime accompanies a visual indicator as a warning to the driver. The ACC system will not operate if the radio amplifier fails.

Brake Pedal Position (BPP) Sensor

The brake pedal position (BPP) sensor helps the BCM determine when pressure is being applied to the brake by the driver stepping on the brake pedal. The BPP sensor receives a low reference signal and a 5-volt reference from the BCM. When the brake is applied, a signal is applied from the BPP sensor through the BPP sensor signal circuit to the BCM. The BCM utilizes this signal in deciding when to command the activation of the stop lamps. The BCM continuously sends signals via the GMLAN serial data circuit to the EBCM and the ECM reflecting the brake pedal position status. This will include the initial brake travel signal required for the activation of the ACC system. The ACC system will not engage unless the initial brake pedal travel signal is valid and received by the BCM. When the BCM brake pedal position signal indicates that brake pedal pressure is being applied by the driver when the ACC system is engaged, the ECM immediately disengages the ACC system. Re-engaging the ACC system will require the driver pressing the set or resume switch. Refer to Brake Pedal Position Sensor Calibration and Exterior Lighting Systems Description and Operation for more information on the brake pedal pressure sensor.

Accelerator Pedal

Deceleration of the ACC vehicle to maintain a certain distance and speed while a slower moving vehicle is in its path is achieved through throttle control by the ECM and the application of light automatic braking by the EBCM. During automatic braking the ECM is commanded to release the throttle by the DSCC. The DSCC via the GMLAN serial data circuit requests the ECM to release the throttle from the currently controlled cruise position. At the end of automatic braking, the ECM will control the vehicle speed to the current set vehicle speed. Driver throttle override occurs when the driver of the ACC vehicle depresses the accelerator pedal with the intention of requesting greater speed than the current throttle position. An example is an ACC vehicle driver stepping on the accelerator for a passing maneuver. The ECM continuously monitors the throttle and reports a throttle override condition. When no throttle override is present, automatic braking is allowed. When throttle override is detected by the ECM, automatic braking in not allowed to affect the vehicle acceleration.

Cruise Control Switch

The cruise control switch, functionally is a common feature that is shared between the Adaptive Cruise Control (ACC) System and the regular cruise control system. The ACC system will not operate if any cruise switch fails. The cruise control switch comprises the following cruise control function switches:

The cruise control function switches are arranged in a resistive ladder design whereby each switch function is set up with different resistance values. The body control module (BCM) through the cruise control switch signal circuit detects a predetermined voltage value when any cruise control switch function is activated. The associated cruise control function signal detected by the BCM is then sent to the engine control module (ECM) as a General Motor local area network (GMLAN) serial data circuit message. The ECM on receiving the message provides the cruise control function requested by the BCM. The ECM is responsible for recognizing and responding to cruise control switch requests sent by the BCM. The cruise control function switches are used by the ECM to communicate to the distance sensing cruise control module (DSCC) the driver selected vehicle speed. The driver selected vehicle speed is communicated through GMLAN serial data circuit to the DSCC and the BCM. The ACC system engages and adjusts vehicle speeds based on the activation of the following cruise control function switches:

On/Off Switch

The BCM monitors the On/Off switch status and makes a determination that the On/Off switch is activated based on a predetermined voltage value at the cruise control switch signal circuit. The On/Off switch state is then relayed to the ECM via the GMLAN serial data circuit. The ECM will recognize and communicate the On/Off switch input to the DSCC. When the On/Off switch is turned ON, it will cause the ACC system to enter either STANDBY ENABLED or STANDBY DISABLED state. The STANDBY ENABLED state indicates that every condition required for the ACC system to function have been met but the ACC is not yet engaged. When in the STANDBY DISABLED state, all conditions necessary for the ACC to function has not been met. When the On/Off switch is turned OFF, ACC will enter the DISABLED state. ACC will not be active in the DISABLED state. When automatic braking is active and the ACC On/Off switch is turned OFF, ACC will delay entering the DISABLED state.

Set/Decrease Switch

The ACC system is engaged when the vehicle driver presses and releases the set/decrease switch. The engaged state of the ACC system can only be entered when the On/Off switch is turned ON. When the set/decrease switch is pressed, the driver selected speed is set to the current vehicle speed by the ECM. The vehicle speed must be above 40 km/h (25 mph). The current driver selected speed is displayed by the head-up display (HUD). While in the engaged state, the driver selected vehicle speed and following distance can be adjusted. Pressing the set/decrease switch when the ACC system is engaged allows the driver to decrease the driver selected vehicle speed. Pressing and holding the set/decrease switch will allow the vehicle to decelerate from the current set vehicle speed without deactivating ACC. The Tap-Down function occurs by momentarily pressing and releasing the set/decrease switch when ACC is engaged. With the Tap-Down function, the driver selected speed is decreased by 1 km/h (1 mph) each time the set/decrease switch is pressed.

The Resume/Increase Switch

When in the resume/increase state, ACC is active and the previously set driver selected speed has not been cleared. The resume/increase switch is used to increase the driver selected speed when ACC is active. The extent to which the driver selected speed can be increased from the resume/increase switch depends on how long the switch is pressed. The presence of a slower moving vehicle in the path of the ACC vehicle will limit the extent to which the driver selected speed can be achieved. If there is no preceding vehicle in front limiting the ACC vehicle acceleration, the current vehicle speed attained is the new driver selected speed. The current driver selected speed is displayed by the HUD. Acceleration is terminated when the resume/increase switch is released. Momentarily pressing and releasing the resume/increase switch will result in the Tap-Up function. With the Tap-Up function, the driver selected speed is increased in increments of 1 km/h (1 mph).

Gap Up/Down Switch

The gap up/down switch allows the driver to determine how closely the adaptive cruise control (ACC) vehicle follows a target vehicle while ACC is engaged. When the ACC vehicle speed is being limited due to a slower travelling vehicle, the ACC vehicle speed is automatically controlled to the follow speed limit. The gap switch has 6 following distance selections that range from 1-2 seconds. The gap switch following distance between the ACC vehicle and the target vehicle is expressed in time as opposed to actual distance. The distance maintained for a selected gap will vary based on vehicle speed. The faster the vehicle speed, the further back you will follow. The gap up/down switch is hard-wired to the body control module (BCM) and voltage is provided to the switch from the BCM via the gap up/down ignition 1 voltage circuit. Based on voltage variations, the BCM is able to read the selected gap up/down switch selection and communicates the switch status on the GMLAN serial data circuit to the distance sensing cruise control module (DSCC). The gap up/down switch is a 3-position momentary switch - Center, Gap Up and Gap Down - with the following valid signal values:

The initial push of the gap switch recalls the current setting and activates the display. Subsequent pushes of the gap switch will change the gap setting. Momentarily pressing the gap up/down switch will adjust the switch to the desired gap setting. When the voltage from the gap up/down switch circuit is in an invalid range, the BCM will default to increasing the gap value.

Cruise Indicators and Messages

SERVICE RADAR CRUISE

The distance sensing cruise control module (DSCC) commands the display of the SERVICE RADAR CRUISE message in the driver information center (DIC) when it detects a malfunction in the Adaptive Cruise Control (ACC) System. The DSCC sends a request to the body control module (BCM) via the GMLAN serial data circuit to display the SERVICE RADAR CRUISE message in the DIC. The DIC displays the SERVICE RADAR CRUISE message when it receives a class 2 serial data request from the BCM. The SERVICE RADAR CRUISE is displayed in the DIC only when a diagnostic condition is present, the cruise switch is in On position, the vehicle speed is above 40 km/h (25 mph), and cruise is engaged or attempted to be engaged. When the message is displayed in the DIC the ACC system disengages. The DIC sounds an internal chime anytime it displays the SERVICE RADAR CRUISE message.

CRUISE NOT READY

The DSCC commands the display of the CRUISE NOT READY message in the DIC when ACC cannot engage due to a temporary condition. The ACC vehicle conditions that prompt the display of the CRUISE NOT READY message are temporary and do not require service. If no target is identified by the forward looking sensor (FLS) and cruise is attempted to be engaged, the CRUISE NOT READY message will be displayed in the DIC until the FLS is able to identify an accepted target. CRUISE NOT READY message is also displayed in the DIC when the DSCC is too hot and the brakes are too hot. The DIC sounds an internal chime anytime it displays the CRUISE NOT READY message.

CLEAN RADAR

The CLEAN RADAR message displays in the DIC when the DSCC detects a blockage of the FLS and cruise is engaged or attempted to be engaged. The FLS may be blocked by snow, ice, dirt, heavy rain or road spray. The DSCC commands the display of the CLEAN RADAR message via a GMLAN serial data circuit request to the BCM. The DIC displays the CLEAN RADAR message when it receives a class 2 serial data request from the BCM. When the CLEAN RADAR message is displayed in the DIC, safely park the vehicle and turn OFF the ignition. Clean the driver side front fascia lens to eliminate the blockage. It may be necessary to clean both the outside surface of the lens, the inside surface of the lens and the DSCC surface. Refer to Distance Sensing Cruise Control Maintenance for more cleaning information. It is important to turn the ignition OFF before cleaning any of the named surfaces. This is because the CLEAN RADAR message may still display in the DIC after cleaning the 3 surfaces. Cycling the ignition to OFF for 10 seconds is necessary to clear the CLEAN RADAR indicator if the indicator remains ON in the DIC. The DIC sounds an internal chime anytime it displays the CLEAN RADAR message. In rare instances, the target characteristics or a vertically misaligned FLS may trigger the activation of the CLEAN RADAR message in the DIC. Refer to Distance Sensing Cruise Control Aiming.

Cruise Engaged Indicator

The ACC engaged indicator is displayed in the head-up display (HUD) when the ACC is engaged by pressing the set/decrease switch. When the set/decrease switch is pressed by the driver, the BCM forwards the switch state to the engine control module (ECM) over the GMLAN serial data circuit. The ECM will use the switch input information from the BCM to determine the driver intended vehicle speed. The ECM communicates to the DSCC over the GMLAN serial data circuit the ACC engaged state and the driver selected speed. When the DSCC receives the ECM message indicating that ACC is active, the DSCC commands the display of the ACC engaged indicator via a GMLAN serial data message to the BCM. The HUD displays the ACC engaged indicator when it receives a class 2 serial data message from the BCM requesting the display. The driver may have to adjust the position of the HUD or the intensity of the display to see the information being displayed properly.

Set Speed

The ACC vehicle set speed is displayed at all times in the primary or secondary display of the HUD when ACC is engaged. The set speed is displayed in the primary HUD display for a few seconds after the initial engagement of ACC or a change in the set speed has just occurred. When, the set speed display time in the primary HUD display elapses, the set speed display is moved to the secondary HUD display. The set speed is also moved to the secondary display when a new ACC related message needs to be displayed. The DSCC set speed display request is sent to the BCM via the GMLAN serial data circuit. The HUD displays the set speed when it receives a class 2 message from the BCM requesting the set speed displayed in the HUD. The HUD controls when the set speed is displayed in the primary or secondary HUD display.

Follow Distance

The HUD displays the driver selected following distance when ACC is engaged and the gap up/down switch is active. The current follow distance setting is displayed in the HUD for a few seconds after the gap up/down switch is pressed to increase or decrease the following distance. The DSCC follow distance display request is sent to the BCM via the GMLAN serial data circuit. The HUD displays the follow distance when it receives a class 2 message from the BCM requesting the follow distance displayed in the HUD. The HUD will not display the follow distance if an indicator with a higher priority needs to be displayed in the HUD.

CRUISE SPEED LIMITED

The CRUISE SPEED LIMITED indicator displays in the HUD when the DSCC detects that the ACC vehicle is travelling at a speed outside the operational range of the FLS and the vehicle speed is being reduced below the driver set speed. The DSCC limits the vehicle speed in order to stay within the acceptable speed limitations of the FLS. The DSCC also limits the vehicle speed in order to adjust the vehicle speed for the chosen gap switch setting. The high speed limit of the ACC system is 186.7 km/h (116 mph). The DSCC requests the display of the CRUISE SPEED LIMITED indicator via a GMLAN serial data message to the BCM. The HUD displays the CRUISE SPEED LIMITED indicator when it receives a class 2 serial data message from the BCM. With a maximum following distance setting, the maximum operating speed will be limited to 160.9 km/h (100 mph). Selecting a smaller following distance will allow greater operating speeds up to a maximum of 186.7 km/h (116 mph).

Vehicle Ahead Indicator

The vehicle ahead indicator is displayed in the HUD when the FLS identifies an in-path vehicle. The vehicle ahead indicator is a warning to the driver that a vehicle is ahead within a distance of 100 meters (109.3 yards). The indicator also serves as a feedback to the driver that the FLS is functioning properly. The DSCC commands the display of the vehicle ahead indicator via a GMLAN serial data message to the BCM. The HUD displays the vehicle ahead indicator when it receives a class 2 serial data message from the BCM. The vehicle ahead indicator only displays with ACC active and may sometimes display for stationary road objects.

TIGHT CURVE

The TIGHT CURVE indicator is displayed in the HUD when the DSCC reduces the vehicle speed for a curve in the road. The tight curve situation exists when the curve of the road extends outside the field of view of the FLS such that the FLS cannot see 100 meters (109.3 yards) ahead. The degree to which the vehicle speed is reduced depends on the extent the curve on the road reduces the usable range of the FLS field of view. In a tight curve situation, the ACC vehicle speed may be reduced even when there is a target vehicle in the path of the ACC vehicle. The DSCC uses an internal algorithm to control the vehicle speed to the radius of the curvature of the road. The DSCC requests the display of the TIGHT CURVE indicator via a GMLAN serial data message to the BCM. The HUD displays the TIGHT CURVE indicator when it receives a class 2 serial data message from the BCM. Since the TIGHT CURVE indicator is only displayed when the vehicle speed is reduced for a curve, the driver may notice a delay between entering the curve and the display of the TIGHT CURVE indicator.

Driver Alert

The driver alert indicator warns the driver of a certain road or vehicle conditions that require his attention. When the driver alert indicator flashes in the HUD it is accompanied by an audible warning from the audio amplifier. The driver alert indicator flashes in the HUD and the audible warning sounds when one of the following occurs:

The DSCC requests the driver alert indicator and the audible warning via a GMLAN serial data message to the BCM. The BCM then sends a class 2 message to the HUD and to the audio amplifier requesting the driver alert indicator and the audible warning to be activated.

Cruise Engaged

The adaptive cruise control (ACC) system will engage and adjust vehicle speeds based on the activation of the following cruise switches:

ACC will not engage if any inhibit criteria is active. Also, the driver must step on the brakes at each ignition cycle before attempting to engage ACC. The engine control module (ECM) looks to the body control module (BCM) for the brake initial travel achieved signal indicating that the driver has stepped on the brakes before attempting to engage ACC.

The vehicle speed must be above 40 km/h (25 mph) and below 188.3 km/h (117 mph) for the ACC system to be engaged. In the engaged state, the ACC system allows the driver to override the controlled vehicle speed temporarily while still remaining in the engaged state.

Cruise Inhibited

DSCC Inhibits

The distance sensing cruise control module (DSCC) inhibits the adaptive cruise control (ACC) system when any of the following conditions exists:

ECM Inhibits

The engine control module (ECM) inhibits the ACC system operation when any of the following conditions exists:

Cruise Disengaged

The Adaptive Cruise Control (ACC) System disengages when any of the following occurs:

Pressing the brake pedal while ACC is engaged will disengage the ACC System.

Other Adaptive Cruise Control (ACC) Features

Automatic Alignment

The Adaptive Cruise Control (ACC) System is equipped with an internal forward looking sensor (FLS) automatic horizontal alignment feature. This feature can not be used for vertical alignment. For proper operation of the ACC System, the FLS must be well aligned to the vehicle. The FLS alignment to the vehicle is continuously corrected and adjusted as necessary during the ACC vehicle operation. To achieve a complete automatic FLS alignment, the ACC vehicle has to be driven on a road above 56 km/h (35 mph) with acceptable stationary objects like mail boxes, road signs, trees, ramps and poles etc. The distance that the vehicle needs to be driven to achieve a complete automatic alignment, depends on the number of stationary objects encountered on the road that the vehicle is travelling. The more stationary objects encountered, the quicker the FLS will achieve automatic alignment. At least 40 acceptable stationary objects must be encountered for proper alignment. When the distance sensing cruise control module (DSCC) is replaced with a new module, it is necessary for the vehicle to be driven until the internal automatic alignment is complete. The scan tool is equipped to display the automatic alignment status and the degree of alignment error or skew of the FLS. A DTC C1002 sets in the DSCC when the degree of error or skew is 2.5 degrees or over.

It is important when performing a wheel alignment service on a vehicle equipped with the ACC System, to change the Auto Alignment Learn Status parameter in the DSCC scan tool data list to Not Aligned. The Auto Alignment Learn Status parameter of the DSCC needs to read Not Aligned to allow the FLS to automatically align to the vehicles new wheel alignment setting. Driving the vehicle in an area with stationary objects will cause the FLS to automatically align horizontally to the vehicles new wheel alignment setting.

Mechanical Alignment

Mechanical alignment must be used for vertical alignment. Proper vertical alignment is achieved with a bubble level tool rested against the front face of the FLS, with the bubble centered. When the alignment of the FLS is not achieved, an out of alignment diagnostic, DTC C1002 is set by the DSCC. The typical horizontal alignment value of the FLS is 0-2 degrees, but it is highly recommended to be as close to 0 degrees as possible. The DSCC diagnostic, DTC C1002 sets when at least 2.5 degrees of skew or error of the FLS is present. Refer to Distance Sensing Cruise Control Aiming for more information on how to aim and align the FLS. An out of alignment condition may be as a result of tampering or damage to the FLS, the FLS mounting structures or the FLS adjuster settings. An out of alignment condition may also be as a result of damage to the front end of the vehicle or merely as a result of wear and tear. Refer to Distance Sensing Cruise Control Module Replacement and Cruise Control Vehicle Distance Module Sensor Replacement on how to properly locate and mount the ACC module and the FLS.

Cruise Control Description and Operation Conventional Cruise

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:

Cruise Control Engaged

The Cruise Control System will engage and adjust vehicle speeds, based on the activation of the following cruise control switches:

The body control module (BCM) monitors the signal circuit of the cruise control switches. The BCM relays the cruise control switch status to the engine control module (ECM) via the GMLAN 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 throttle actuator control (TAC) motor in order to maintain the vehicle speed. For further review of the TAC system, refer to Throttle Actuator Control (TAC) System Description for the 4.4L engine.

Ignition voltage is supplied to the cruise control switch from the 2-ampere STRG COL SW fuse located in the integrated BCM fuse block. 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 any cruise control function switch being activated. When the normally open cruise control on/off switch is turned ON, the switch closes and the BCM detects a predetermined voltage signal on the cruise control set/coast and resume/accel switch signal circuit. The BCM sends a GMLAN serial data message to the ECM indicating that the on/off switch is active. Similarly, when the + RES switch or the - SET switch are pressed, the BCM detects the predetermined voltage signal on the cruise control set/coast and resume/accel switch signal circuit. 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 GMLAN serial data message to the BCM. The BCM then sends a class 2 serial data message to the head-up display (HUD) in order to illuminate the Cruise Speed SET XXX message.

The - SET switch or the + RES switch will remain inactive when the BCM has not received the predetermined voltage signal from the On/Off switch. 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 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 pressing the + RES 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 engine control module (ECM) disengages the cruise control operation based on the signals from the following switches:

The BPP sensor is mounted on the brake pedal bracket. Pressing the brake pedal while the cruise control is engaged will disengage the Cruise Control System. The body control module (BCM) monitors the BPP sensor via the brake pedal position sensor signal circuit. The BCM sends a GMLAN serial data message to the ECM and to the transmission control module (TCM) indicating the position of the brake pedal. For further information on the BPP sensor, refer to Exterior Lighting Systems Description and Operation or to Brake Pedal Position Sensor Calibration .

The Cruise Control System will also disengage when the cruise control On/Off switch is switched OFF or 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 GMLAN serial message to the BCM. The BCM then sends a class 2 serial data message to the HUD in order to turn OFF the Cruise Speed SET XXX message.

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.

Cruise Control Inhibited

The engine control module (ECM) inhibits the cruise control operation when any of the following conditions exist: