Principles of Operation

Forward Collision Warning

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

The forward collision warning system is a safety feature that alerts the driver of a high risk collision. In the event of a possible collision, the Head Up Display (HUD) module flashes, a chime from the Instrument Panel Cluster (IPC) activates, and the Audio Control Module (ACM) volume mutes.

The forward collision warning system is activated when the vehicle is moving forward at a speed greater than 8 km/h (5 mph). The Cruise-Control Module (C-CM) determines the distance and relative speed of the vehicle that is in the path of travel, utilizing a radar sensor (integral to the C-CM) to detect other vehicles that are moving in the same direction. If the C-CM determines that a collision is possible, the C-CM sends a serial message over the High Speed Controller Area Network (HS-CAN) to the HUD module and the LEDs internal to the module flash.

The forward collision warning system and audible warning chime can be enabled and disabled through the message center in the IPC. The system reverts to on each ignition cycle. The HUD module and/or chime activates briefly to confirm the last setting. The sensitivity of detection can also be changed in the message center from a high sensitivity ( ----->) to a low sensitivity ( ->).

When a MyKey(TM) is in use, MyKey(TM) turns on the forward collision warning and will not allow the MyKey(TM) user to disable the audio or visual forward collision warning system. However, the MyKey(TM) user is able to adjust the forward collision warning sensitivity.

The forward collision warning system works in conjunction with the adaptive cruise control system. If the vehicle is utilizing the adaptive cruise control feature and is at its maximum braking capability, the C-CM sends a "forward collision warning display" message over the HS-CAN to the HUD module and the LEDs flash. The C-CM sends a message over the HS-CAN of "forward collision warning audio level" to the IPC, which activates a chime. The C-CM sends a message over the HS-CAN of "forward collision audio mute" to the IPC. The IPC gateways the message over the Medium Speed Controller Area Network (MS-CAN) to the ACM and the volume mutes. For more information on the adaptive cruise control system, refer to Fire Suppression System.

There are certain situations when the warning LEDs cannot be seen, such as strong sunlight or when sunglasses are being worn. The HUD module has a temperature sensor circuit that is integral to the module that senses the temperature of the LEDs internal to the module. When a high passenger compartment temperature such as strong sunlight, is sensed by the temperature sensor, the warning LEDs can be temporarily disengaged. If this occurs, only the audible warning chime is used. Warnings may not appear if the distance to the vehicle ahead is very small or if the steering wheel and pedal movements are large, for example, due to a very active driving style.

Network Communication

The following forward collision warning system components communicate via the HS-CAN:

- HUD module
- C-CM
- ABS module
- IPC

HS-CAN Module Communication Message Chart

NOTE: While there are numerous messages internal to the HUD module, the following messages are utilized by the forward collision warning system in conjunction with outside systems.