Turn Signal Lamps

The turn signal lamps system includes the SCCM microcontroller, the EMIC, the BCM and the multifunction switch on the steering column. The front turn signal lamp bulbs each have a path to ground at all times through their connection to the Front End Module (FEM) wire harness. The FEM wire harness has takeouts with eyelet terminals that are secured by ground screws to the body sheet metal within the engine compartment. The rear turn signal lamp bulbs have a path to ground at all times through a takeout and eyelet terminal of the body wire harness that is secured by a ground screw to the body sheet metal within the passenger compartment. On vehicles with the optional outside rear view mirror lamp modules, the lamp modules receive a path to ground from their respective driver or passenger door module.

The SCCM microcontroller monitors a hardwired multiplex input from the multifunction switch to determine the status of the turn signal switch, then sends the appropriate electronic turn signal switch status  messages to the BCM over the CAN data bus. The BCM responds to these messages by controlling a battery voltage output and the flash rate for either the right or left turn signal lamps. The BCM also sends the appropriate electronic messages back to the EMIC to control the illumination and flash rate of the right or left turn signal indicators, as well as to control the click rate of an electromechanical relay soldered to the EMIC electronic circuit board that emulates the sound emitted by a conventional turn signal flasher. On vehicles with the optional outside rear view mirror lamp modules, the BCM also sends the appropriate electronic messages over the CAN bus to the driver and passenger door modules to control the illumination and flash rate of those lamps.

The EMIC also provides a turn signal ON warning  that will generate repetitive chimes to indicate that a turn signal has been active continuously for 1.6 kilometers (1 mile) with the vehicle speed greater than 22 km/h (15 mph). Vehicles built for markets other than the United States and Canada have a revised distance threshold of 4 kilometers (2.49 miles) for this feature. The chime will continue until the turn signal input becomes inactive or until the vehicle speed message indicates that the speed is less than 22 km/h (15 mph), whichever occurs first.