Adaptive Cruise Control: Notes
DESCRIPTION
The following components are part of the Adaptive Cruise Control (ACC) system:
| 1. | Refer to FORWARD FACING CAMERA MODULE (FFCM) . |
| 2. | Refer to STEERING WHEEL SWITCH (SWS) . |
| 3. | Refer to ADAPTIVE CRUISE CONTROL (ACC) RADAR . |
| - | Refer to POWERTRAIN CONTROL MODULE (PCM) . |
| - | Refer to STEERING COLUMN CONTROL MODULE (SCCM) . |
| - | Refer to INSTRUMENT PANEL CLUSTER (IPC) . |
| - | Refer to BODY CONTROL MODULE (BCM) . |
| - | Refer to RADIO . |
| - | Refer to ADAPTIVE CRUISE CONTROL (ACC) RADAR . |
| - | Refer to TRANSMISSION CONTROL MODULE (TCM) . |
| - | Refer to ELECTRONIC SHIFT MODULE (ESM) . |
OPERATION
The ACC system:
- Is a convenience feature (not a safety system) that allows the vehicle operator to keep cruise control engaged while driving without having to constantly reset the system with approaching slower moving vehicles.
- Uses data from the FFCM to detect vehicles in the forward path of the host vehicle.
- Detects the moving, stopped and stationary vehicles that are in the path of the host vehicle.
- A moving vehicle is a vehicle that has a speed greater than zero.
- A stopped vehicle is a vehicle that had a greater speed than zero then came to a stop.
- A stationary vehicle is a vehicle that has never been determined to have a speed greater than zero.
- Will automatically decrease the speed of the host vehicle by sending torque requests to the PCM via the ABS module if a slower moving target vehicle is detected in the path of the host vehicle.
- Decelerates the speed of the vehicle to the speed of the target vehicle while maintaining a driver selected time-gap (distance) from the target vehicle.
- Restores the vehicle back to the original set speed by accelerating smoothly and comfortably when the target vehicle is no longer present.
- Is active at speeds above 30 km/h (20 mph) and up to speeds of 200 km/h (100 mph).
- Also controls the standard cruise control operations. The vehicle operator can chose which system (Standard, ACC) to use.
The vehicle operator controls all ACC system features through the SWS pod on the face of the right horizontal spoke of the steering wheel. When a push button of the SWS pod is depressed, it provides a switch input to the SCCM.
The SCCM reads the speed control switch input, then relays an electronic speed control switch status message to the PCM and to the ACC module over the Controller Area Network (CAN) data bus while using the BCM to gate messages between the different networks. The PCM and ACC modules continually monitor these inputs as well as electronic wheel speed message inputs from the ABS module, electronic gear selector message inputs from the TCM, video data from the FFCM and numerous hard wired inputs including the brake (stop) lamp sensor, then provides the appropriate electronic message and hard wired outputs to invoke the requested electronic speed control features.
Using the MODE push button of the speed control switch pod on the face of the right horizontal spoke of the steering wheel, the vehicle operator can choose between adaptive speed control and conventional speed control modes of operation. When in the adaptive speed control mode, the vehicle operator can use the DISTANCE push button of the speed control switch pod to select from one of three distance settings for the adaptive cruise system to maintain. These settings equate to the time in seconds separating the vehicle from a preceding vehicle. The FFCM and the ACC module share a private bus allowing data fusion to occur within the ACC module. The ACC module then uses this information to send electronic message outputs to the ABS, the TCM and the PCM to maintain the selected separation distance.
CAUSES FOR ACC TO BE DISABLED
Any issues with the following external inputs can cause the ACC system to become disabled:
- Vehicle dynamic data including yaw rate, longitudinal acceleration, steering angle input and wheel speed
- Brake switch/sensor/pedal
- PCM
- Transmission/Transmission Control Module (TCM)
- IPC
- Cruise control switch pods
- ABS module
- BCM
- ACC module
- FFCM
Be sure to always check for DTCs or IPC cluster messages in the event of the ACC system not functioning.
The PCM and ACC modules continuously monitor all of the speed control system electrical circuits to determine the system readiness and accuracy. If the PCM or ACC module detects a monitored system fault, it sets and stores a DTC. The PCM and ACC components use On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with the diagnostic scan tool using the CAN data bus. This method of communication is used for control of the Malfunction Indicator Lamp (MIL) in the IPC and for system diagnosis and testing through the data link connector located on the driver side lower edge of the instrument panel.
PREFILL
Under normal circumstances, there is space between the brake pads and the brake rotors to prevent the pads from wearing out prematurely. This space between the pads and rotors increases the response time during any situation which may require emergency braking. The brake prefill prepares the system for braking by moving the pads closer to the rotor thus improving braking response time. The ACC module controls the activation and deactivation of the brake prefill. The ESC module provides the brake prefill status to the ACC module. The brake prefill:
- Will not illuminate the brake lamps.
- Is performed by the ESC module located within the ABS module.
- Will cause no audible brake noise.
- Will cause no vehicle deceleration.
DRIVER OVERRIDE
- The driver will always have the ability to override the ACC system by pressing the throttle.
- The ACC module monitors for the override signal.
OVERTAKE AID
- When a vehicle, that is in the Engaged or Set stage, is trailing a slower moving vehicle, the system provides the Overtake Aid when the driver activates the turn signal indicator. The Overtake Aid consists of additional amounts of acceleration while still trailing the vehicle to aid a lane shift maneuver.
- The ACC module receives the status of the turn signal indicator from the BCM.
- The Overtake Aid provides for left hand or right hand drive locations.
- The ACC module determines the direction of traffic flow by observing oncoming traffic and then automatically provides Overtake Aid to the proper side of the vehicle.
TAKE OVER REQUEST
- If the ACC system is unable to maintain the following distance by applying maximum deceleration, a Take Over Request is issued by the ACC module.
- This request is initiated by the system by simultaneously sending an audible and visual warning to the IPC, along with an audible warning to the audio system.
- A Take Over Request can be initiated by the ACC module in the condition where there is a close cut-in vehicle from an adjacent lane to the lane of the ACC host vehicle.
FUEL SHUTOFF DISABLEMENT
- As a way of saving fuel and improving fuel economy, the PCM may shut off or reduce the amount of fuel being supplied to the engine while the vehicle is in certain driving conditions.
- Although this reduces the amount of fuel being used by the vehicle, it can create driver discomfort in the form of a system delay when the fuel is turned back on and the ACC module is requesting acceleration.
- The ACC module sends a signal to the PCM in an attempt to disable fuel shutoff or restrictions during certain ACC driving situations.