Skip to content
Tahoe / Yukon Service Manual

Adaptive Cruise Control Description and Operation (with UGN)

Adaptive Cruise Control Description and Operation (with UGN) The adaptive cruise control 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 adaptive cruise control system is the ability to detect the presence of a vehicle in the path of the adaptive cruise control vehicle. Adaptive cruise control retains the existing cruise control feature that controls the vehicle speed to the driver selected speed. However, adaptive cruise control allows a driver to set and maintain a following distance to the preceding nearest vehicle in the path ahead. The K124 Image Processing Module controller calculates a follow speed limit to ensure an acceptable distance is maintained to the preceding vehicle in front, should one be present. The adaptive cruise control system automatically adjusts the speed when the vehicle comes up behind a slower travelling vehicle in front. The system applies limited automatic braking and throttle control without driver input when necessary to maintain the set following distance. The preceding vehicle’s speed and acceleration along with the active cruise control vehicle speed and acceleration and the distance between the two vehicles are factors used by the K124 Image Processing Module controller to determine the follow speed limit. The vehicle speeds up to the original driver selected set speed when the pathway becomes clear without driver input. The adaptive cruise control functionality depends on various modules on the vehicle to function and each module performs a function that is critical to the proper operation of the adaptive cruise control system. Adaptive cruise control will not operate if any components fail. Communication between modules is via serial data. The following is a functional description of the K124 Image Processing Module and the other associated components: K124 Image Processing Module B233B Forward Radar Sensor Module - Long Range K9 Body Control Module K20 Engine Control Module K160 Brake System Control Module K71 Transmission Control Module P16 Instrument Panel Cluster Control Module Cruise Control Switch Gap Switch K124 Image Processing Module The K124 Image Processing Module analyzes data from various modules, sensors, and switches to provide enhanced safety features. In addition to enhanced safety features, the K124 Image Processing Module provides the adaptive cruise control system functionality. The K124 Image Processing Module analyzes data from the B233B Forward Radar Sensor Module - Long Range to identify and classify objects in the road environment. The system scans the road environment to detect targets within its specified field of view. The K124 Image Processing Module then sends throttle and/or brake commands to the K20 Engine Control Module and K160 Brake System Control Module via serial data in order to control the vehicle acceleration/deceleration based on the data from the modules. The K20 Engine Control Module and K160 Brake System Control Module provide throttle control and automatic braking needed for proper cruise speed adjustment. The following is a list of the K124 Image Processing Module functions pertaining to the adaptive cruise control functionality: The K124 Image Processing Module processes the road environment to get data concerning any vehicle ahead of the adaptive cruise control vehicle. Detection, parameter estimation, tracking, object classification and diagnostics are the primary functions. When an object is detected, the controller calculates the object range, range rate, acceleration and azimuth angle parameters. The K124 Image Processing Module performs adaptive cruise control state processing automatically – distance control or speed control. The adaptive cruise control operates in two possible states – cruise or follow. The normal operating state is cruise, whereby the vehicle speed is controlled to match the driver selected set speed. When a preceding forward target is identified, the adaptive cruise control system will automatically transition into the follow speed state to provide proper lane spacing behind the target vehicle in front. The preceding vehicle’s speed and acceleration, with the adaptive cruise control vehicle speed, acceleration and distance between the two vehicles will be used to determine the adaptive cruise control follow speed limit. The adaptive cruise control follow speed limit will ensure that an acceptable distance is maintained to the preceding vehicle. The K124 Image Processing Module determines the follow speed limit for throttle control by the K20 Engine Control Module . The K124 Image Processing Module arbitrates the adaptive cruise control system brake and throttle control between the K160 Brake System Control Module and the K20 Engine Control Module . The K124 Image Processing Module requests brake light activation during automatic braking. The K124 Image Processing Module provides operational feedback to the vehicle driver. The K124  Image Processing Module sends signals for telltales and messages to be displayed on the P16  Instrument Panel Cluster Control Module or driver information center. B233B Forward Radar Sensor Module - Long Range The B233B Forward Radar Sensor Module - Long Range is located behind the front fascia and is used in the 30–200 m (98–656 ft) range. The B233B Forward Radar Sensor Module - Long Range communicates with the K124 Image Processing Module via serial data on CAN 8. In addition to the wiring harness ground, the module is grounded through the mounting bracket. K9 Body Control Module The following are the adaptive cruise control system functions provided by the K9 Body Control Module: The K9 Body Control Module reads all cruise control switches and the gap switch. The K124 Image Processing Module monitors a variety of user operated switches from the K9 Body Control Module switch status information sent via CAN. The K9 Body Control Module illuminates the brake light based on a CAN message from the K124  Image Processing Module during automatic braking. The K9 Body Control Module measures the brake pedal position and sends brake pedal travel status via CAN to the K20 Engine Control Module . The K20 Engine Control Module disengages the adaptive cruise control system when the brake is applied by the driver pressing the brake pedal. K20 Engine Control Module The following are the adaptive cruise control system functions performed by the K20 Engine Control Module: The K20 Engine Control Module provides the electronic throttle control to the adaptive cruise control System. The K20 Engine Control Module is also responsible for determining when a driver is overriding the adaptive cruise control throttle position by pressing the accelerator pedal. The K20 Engine Control Module processes the cruise control switch requests received via CAN from the K9 Body Control Module. Engaging and disengaging the adaptive cruise control system are functions performed by the K20 Engine Control Module . The K20 Engine Control Module determines the driver selected vehicle speed. Unless the adaptive cruise control module requests a lower vehicle speed, the K20 Engine Control Module will control the vehicle speed to the driver selected set speed. The K20 Engine Control Module allows automatic braking without disengaging the adaptive cruise control. K160 Brake System Control Module The following are the adaptive cruise control System functions performed by the K160 Brake System Control Module: The K160 Brake System Control Module controls the operation of the Antilock Brake System. The K160 Brake System Control Module provides automatic braking for the adaptive cruise control system. The K124 Image Processing Module will request vehicle deceleration via high speed GMLAN serial data circuit. The K160 Brake System Control Module determines when the driver–applied brake pressure is active. The K160 Brake System Control Module will communicate this status via CAN to the K9  Body Control Module. The K160 Brake System Control Module releases vehicle automatic braking when there is a throttle override by the driver pressing the accelerator. The K160 Brake System Control Module predicts brake temperatures. Due to automatic braking, the brake system may overheat. When the brakes are overheated, the K160 Brake System Control Module requests the adaptive cruise control System to be temporarily shut down by the K20  Engine Control Module until the brakes cool to a normal operating temperature. K71 Transmission Control Module The K71 Transmission Control Module provides a down shift to protect the brakes. When the K71  Transmission Control Module detects some driver braking activity or adaptive cruise control automatic braking activity, the K71 Transmission Control Module down shifts the vehicle transmission to increase engine braking. This helps reduce braking activity, extend brake pad life and reduce brake system overheating. P16 Instrument Panel Cluster Control Module The driver information center is a part of the P16 Instrument Panel Cluster Control Module and displays the adaptive cruise control system warning messages. The K124 Image Processing Module requests messages to be displayed on the driver information center by sending a CAN request to the P16  Instrument Panel Cluster Control Module requesting the display of the warning message. When the message is acknowledged by the driver and the cause of the message resolved, the driver information center turns the message off. The adaptive cruise control system will not operate if the driver information center fails. Cruise Control Switch The cruise control switch, functionally is a common feature that is shared between the adaptive cruise control system and the regular cruise control system. The adaptive cruise control system will not operate if any cruise switch fails. The cruise control switch comprises the following cruise control function switches: On/Off switch Set/decrease switch Resume/increase switch The cruise control function switches are arranged in a resistive ladder design whereby each switch function is set up with different resistance values. The K9 Body Control Module 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 K9 Body Control Module is then sent to the K20 Engine Control Module as a CAN message. The K20 Engine Control Module on receiving the message provides the cruise control function requested by the K9 Body Control Module. The K20 Engine Control Module is responsible for recognizing and responding to cruise control switch requests sent by the K9 Body Control Module. The cruise control function switches are used by the K20 Engine Control Module to communicate to the K124 Image Processing Module the driver selected vehicle speed. The driver selected vehicle speed is communicated through GMLAN serial data circuit to the K124 Image Processing Module and the K9 Body Control Module. The adaptive cruise control system engages and adjusts vehicle speeds based on the activation of the following cruise control function switches: Cruise Control On/Off Switch The K9 Body Control Module monitors the switch signal circuit in order to determine when the On/Off switch is disabled or activated. The K9 Body Control Module detects a predetermined voltage value on the switch signal circuit. The On/Off switch state is then relayed to the K20 Engine Control Module via CAN. The K20 Engine Control Module sends the On/Off switch input status to the K124 Image Processing Module . When the On/Off switch is turned ON, the adaptive cruise control system enters either a standby enabled or a standby disabled mode. The standby enabled mode indicates that every condition required for the adaptive cruise control system to function has been met, but the adaptive cruise control is not engaged. When the adaptive cruise control is in the standby disabled mode, the conditions necessary for the adaptive cruise control system to function has not been met. When the On/Off switch is turned OFF, the adaptive cruise control will enter the disabled mode. The adaptive cruise control will not activate in the disabled mode. Cruise Control Set/Decrease Switch The adaptive cruise control system is engaged when the adaptive cruise control On/Off switch is turned ON and the set/decrease switch is momentarily pressed and released . When the set/decrease switch is pressed, the selected vehicle speed is set to the current vehicle speed by the K20 Engine Control Module . The vehicle speed must be at or greater than 40 km/h (25 MPH). The selected vehicle speed is displayed by the driver information center. While in the engaged state, the selected vehicle speed and the following distance can be adjusted. Pressing and holding the set/decrease switch, when the adaptive cruise control system is engaged, will decrease the selected vehicle speed without deactivating the adaptive cruise control. Momentarily pressing and releasing the set/decrease switch, when the adaptive cruise control is engaged, decreased the selected vehicle speed by 1.6 km/h (1 MPH) for each time that the set/decrease switch is pressed. Cruise Control Resume/Increase Switch The resume/increase switch is used in order to increase the selected vehicle speed when adaptive cruise control is active. The amount selected vehicle 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 adaptive cruise control vehicle will limit the extent to which the selected vehicle speed can be achieved. If there is no preceding vehicle in front, limiting the adaptive cruise control vehicle acceleration, then the vehicle speed that is attained is the new selected vehicle speed. The current selected vehicle speed is displayed by the driver information center. Acceleration is terminated when the resume/increase switch is released. Momentarily pressing and releasing the resume/increase switch will allow the selected vehicle to accelerate in at 1.6 km/h (1 MPH) increments for each time that the resume/increase switch is momentarily pressed. Gap Switch The gap switch allows the driver to determine how closely the adaptive cruise control vehicle follows a target vehicle while adaptive cruise control is engaged. When the adaptive cruise control vehicle speed is being limited due to a slower travelling vehicle, the adaptive cruise control vehicle speed is automatically controlled to the follow speed limit. The gap switch has 3 following distance selections that range from 1–2 s. The gap switch following distance between the adaptive cruise control 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 setting can only be adjusted when the adaptive cruise control system is engaged. The gap switch is hard-wired to the K9 Body Control Module. Based on voltage variations, the K9 Body Control Module is able to read the gap switch selection and communicates the switch status via CAN to the K124 Image Processing Module . The gap switch is a momentary switch. 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. Driver Information Messages Adaptive Cruise Control Temporarily Unavailable The K124 Image Processing Module will send this message if the adaptive cruise control has been disengage or disabled. There are many reasons that can cause this, some will also set DTCs. Check vehicle for DTCs and also check the adaptive cruise control enable and disengage scan tool data. Definitions of parameters can be found in K124 Image Processing Module scan tool information. Service Driver Assist System This message can be set by either the K124 Image Processing Module if there is a problem with the driver assist system or by the memory seat module if there is a problem with the haptic seat circuits. Check vehicle for DTCs. Service Adaptive Cruise Control and Service Front Camera The message is set if the K124 Image Processing Module is not communicating to the P16  Instrument Cluster . Check vehicle for DTCs. Set Speed The adaptive cruise control vehicle set speed is displayed at all times in the driver information center when adaptive cruise control is engaged. The K124 Image Processing Module set speed display request is sent to the P16 Instrument Cluster via the GMLAN serial data circuit. Follow Distance The driver information center displays the driver selected following distance when adaptive cruise control is engaged and the gap switch is active. The current follow distance setting is displayed in the driver information center for a few seconds after the gap switch is pressed to increase or decrease the following distance. The K124 Image Processing Module follow distance display request is sent to the P16 Instrument Cluster via the GMLAN serial data circuit. Vehicle Ahead Indicator The vehicle ahead indicator is displayed in the P16 Instrument Cluster hen the radar identifies an in-path vehicle. The vehicle ahead indicator is a warning to the driver that a vehicle is ahead. The indicator also serves as a feedback to the driver that the radar is functioning properly. The K124  Image Processing Module commands the display of the vehicle ahead indicator via a GMLAN serial data message to the P16 Instrument Cluster . The vehicle ahead indicator only displays with the adaptive cruise control active and may sometimes display for stationary road objects. Adaptive Cruise Control Operation Adaptive cruise control uses the K124 Image Processing Module and B233B Forward Radar Sensor Module - Long Range, which looks directly ahead to monitor vehicles that a driver is following. Adaptive cruise control helps drivers follow a vehicle ahead at the following gap they select — Far, Medium or Near — while they steer. This reduces the driver’s need to frequently brake and accelerate. If the system does not detect a vehicle ahead, adaptive cruise control will resort to traditional cruise control operation. When the system detects a vehicle ahead in the driving lane, the vehicle ahead icon will appear in green on the P16 Instrument Panel Cluster Control Module. When the vehicle detected ahead is within the selected following gap setting, adaptive cruise control can automatically slow the vehicle down and adjust vehicle speed to follow the vehicle ahead at the selected following gap. Like regular cruise control, adaptive cruise control uses ON/OFF, CANCEL, SET and RESUME buttons on the steering wheel. Getting started: To turn adaptive cruise control on, the driver should press the cruise control ON/OFF button. When the system is turned on, the driver information center in the P16 Instrument Panel Cluster Control Module will show a white adaptive cruise control icon. To choose a cruise speed, the driver should press the SET button while driving at the desired speed. The white adaptive cruise control icon will change to green, indicating that adaptive cruise control is engaged. The adaptive cruise control gap switch on the steering wheel lets drivers select a Far, Medium or Near following gap between their vehicle and the vehicle ahead. Both adaptive cruise control i and forward collision alert are set at the same setting. Adaptive cruise control can follow a vehicle ahead to a stop. When the vehicle ahead starts moving again, the driver should check that it is safe to proceed, then continue to automatically follow the vehicle ahead by pressing the accelerator or resume button. If the driver doesn’t respond soon after the stop, the vehicle ahead icon will flash. In addition, an audible notification will sound, or if equipped, the safety alert seat will pulse to remind the driver to check traffic ahead before proceeding. If the adaptive cruise control is controlling speed and detects that the vehicle is approaching a vehicle ahead too quickly and adaptive cruise control cannot apply sufficient braking, such as when vehicles ahead suddenly slow or stop, drivers will receive a forward collision alert to warn them to quickly take action. This alert includes a red flashing visual alert, an audible notification, or, if equipped, the safety alert seat will pulse. If the driver uses the accelerator pedal while adaptive cruise control is active, a driver information center warning message will indicate that automatic braking will not occur. In some vehicles, instead of the message, the green adaptive cruise control icon will change to blue. Switching between cruise control modes (if available): The driver should press and hold the cruise control CANCEL button. The driver will see either the adaptive cruise control icon or the regular cruise control icon on the driver information center. This icon indicates which cruise control mode has been selected. Drivers should check which cruise control icon is displayed before setting their cruise control speed. The driver can end adaptive cruise control by doing any of the following: Stepping lightly on the brake pedal Pressing the cruise control CANCEL button Pressing the cruise control ON/OFF button Adaptive Cruise Control Operational Checks Safety Considerations The system can only apply limited braking. The driver’s complete attention is always required while driving The system may not react to parked, stopped or slow-moving vehicles; the driver should always be ready to take action and apply the brakes Driver should not use adaptive cruise control on winding or hilly roads, on freeway exit or entrance ramps or when trailering. In these driving conditions, the system may not detect the vehicle ahead The system cannot detect traffic lights or traffic signs, so the driver needs to safely brake accordingly whenever approaching an intersection with a traffic light or stop sign If no vehicle ahead is detected, adaptive cruise control will work like regular cruise control When using adaptive cruise control, the driver should keep in mind that the system is designed to follow detected vehicles ahead at a longer distance when traveling at higher speeds than at lower speeds To avoid using adaptive cruise control by accident, advise customers to keep the cruise control button off when they don’t need it. They should press the ON/OFF button and verify that the adaptive cruise control icon is not lit Adaptive cruise control may have difficulty detecting the following objects: Vehicles in front of the driver’s vehicle that have a rear aspect that is low, small or irregular A truck or trailer that has no cargo in the cargo bed Vehicles with cargo extending from the back end Non-standard shaped vehicles, such as vehicle transport, vehicles with a sidecar or horse carriages Vehicles that are low to the road surface Objects that are close to the front of the driver’s vehicle Weather conditions can affect adaptive cruise control: If the vehicle’s interior temperature is extremely high, the P16 Instrument Panel Cluster Control Module may indicate that adaptive cruise control is temporarily unavailable. This can be caused by extreme hot weather conditions. Adaptive cruise control will return to normal operation once the ambient is cooler Conditions that are associated with low visibility, such as rain, snow or road spray, may limit the performance of adaptive cruise control.