Description And Operation

DESCRIPTION 

Courtesy of CHRYSLER GROUP, LLC

The ACC module is a stand-alone forward facing radar module. It is mounted to the vehicle structure, outside the cabin, in a manner allowing for an unobstructed view. The ACC module can operate as a stand-alone Electronic Control Unit (ECU) or can also be used in conjunction with additional forward ranging and object detection sensors in order to provide many driver assistance systems features.

The ACC module and radar sensor communicates with other vehicle modules via both public and private bus networks to provide the following features sets:

• Standard Cruise Control
• Adaptive Cruise Control with Stop and Go (ACC+)
• Forward Collision Warning (FCW)
• FCW with Collision Mitigation (FCW+)
• Full Speed Range Forward Collision Mitigation (FSRFCW+)
• Advanced Brake Assist (ABA)

The ACC module electronic circuitry is sealed and protected within a die cast aluminum housing. A molded plastic cover and a lens or radar dome faces forward through an opening in the center of the front fascia lower. A molded plastic module bezel or mirror cover with a center clearance hole for the module lens snaps over the module and conceals a small square mirror in one corner of the module cover that is used for calibration purposes during the module manufacturing process.

The ACC module includes an applied connector receptacle that is sealed and secured to the module housing with screws and faces downward when installed on the mounting bracket. The ACC module is connected to the vehicle electrical system through a single dedicated takeout and connector of the Front End Module (FEM) wire harness.

OPERATION 

The Adaptive Cruise Control (ACC) module contains the logic circuits and controls many of the features of the adaptive speed control system. The ACC module receives battery voltage on a fused ignition switch output (run) circuit and is grounded at all times through a hard wired remote ground point. These connections allow the ACC module to operate only when the ignition switch is in the ON position. Likewise, the ACC module sleeps whenever the ignition switch is in any position except RUN.

The ACC module is also a Radio Detection And Ranging (RADAR) transceiver. The ACC module transmits electromagnetic signal bursts at an operating frequency of 77 gigahertz. Those signal bursts are scattered by any objects they strike within the 40 degree field of view of the transceiver, which changes the strength and frequency of the signal. The ACC module antenna receives and interprets the returned signals to detect any objects in the path of the vehicle as well as their speed and direction.

The ACC module receives electronic speed control switch status message inputs from the microcontroller integral to the Steering Column Control Module (SCCM) over the Controller Area Network (CAN) data bus. The module also monitors electronic message inputs from the Powertrain Control Module (PCM), the Antilock Brake System (ABS) Module and the Transmission Control Module (TCM).

The ACC module logic processes all of those inputs, then provides the appropriate electronic message outputs over the CAN data bus to the PCM, the TCM and the ABS to control and maintain the separation setting selected by the vehicle operator between the vehicle and any preceding vehicles. The ACC module also provides electronic message outputs to the Instrument Panel Cluster (IPC) and the Electronic Vehicle Information Center (EVIC) to invoke the Forward Collision Warning (FCW) features.

The module also contains an electronic ambient temperature module and a heating element. When appropriate ambient temperatures are sensed, the heating element is energized by the ACC module control circuitry to keep the module lens or radar dome clear of ice and snow accumulations that might otherwise blind the module to proper reception of returned signals.

For those models equipped with the Forward Facing Camera (FFC), the camera provides additional object and environmental information to the radar to support its decision making. If the two readings between the FFC and the ACC radar are not completely identical, the system will become disabled. When the ACC system is paired with the FFC option, this is known as the ACC+ system.

The ACC module microcontroller continuously monitors all of its internal electronics to determine the module readiness. If the ACC module detects a monitored module fault, it sets and stores a DTC. The ACC module uses On-Board Diagnostics (OBD) and can communicate with other electronic modules in the vehicle as well as with the diagnostic scan tool over the CAN data bus. This method of communication is used for control of the indicators and indications provided to the vehicle operator through the IPC and the EVIC. The ACC module is also Flash programmable, allowing the module software to be updated using a diagnostic scan tool.