Turn Signal Indicator - Operation

OPERATION

The turn signal indicators give an indication to the vehicle operator that the turn signal (left or right indicator flashing) or hazard warning (both left and right indicators flashing) have been selected and are operating. These indicators are controlled by transistors on the instrument cluster electronic circuit board based upon the cluster programming and electronic messages received from the Front Control Module (FCM) over the Controller Area Network (CAN) data bus.

Each turn signal indicator Light Emitting Diode (LED) is completely controlled by the instrument cluster logic circuit, and that logic will allow this indicator to operate whenever the instrument cluster receives a battery current input on the fused B(+) circuit. Therefore, each LED can be illuminated regardless of the ignition switch position. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn ON the turn signal indicators for the following reasons:

- Turn Signal Indicator Lamp-On Message - Each time the cluster receives an electronic right or left turn signal-ON message from the FCM over the CAN data bus, the appropriate turn signal indicator will be flashed ON and OFF. The FCM also sends the appropriate electronic message to the cluster to control the flash rate of the turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the cluster electronic circuit board that emulates the sound emitted by a conventional turn signal flasher. The turn signal indicators continue to flash ON and OFF until the cluster receives a lamp-OFF message from the FCM, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Hazard Warning Indicator Lamp-On Message - Each time the cluster receives an electronic hazard warning-ON message from the FCM over the CAN data bus, both turn signal indicators will be flashed ON and OFF. The FCM also sends the appropriate electronic messages to the cluster to control the flash rate of the right and left turn signal indicators, as well as to control the click rate of an electromechanical relay soldered onto the cluster electronic circuit board that emulates the sound emitted by a conventional hazard warning flasher. The turn signal indicators continue to flash ON and OFF until the cluster receives a hazard warning-OFF message from the FCM.
- Turn Signal-On Textual Warning Message - When the cluster detects that a turn signal has been active continuously for 1.6 kilometers (1 mile) with the vehicle speed greater than 22 kilometers-per-hour (15 miles-per hour) a TURN SIGNAL ON textual message and flashing right or left turn signal icon will appear within the instrument cluster reconfigurable dot matrix display and a chime tone will be sounded.
- Lamp Out Mode - If the FCM detects an ineffective turn signal lamp or circuit, it increases the flash rate for the remaining operative turn signals and sends an electronic message to the instrument cluster. The instrument cluster then increases the flash rate of the turn signal indicators and the click rate of the electromechanical relay to provide an indication of the problem to the vehicle operator.
- Self Test - Each time the cluster is put through the self test, the turn signal indicators will be turned ON, then OFF again during the bulb check portion of the test to confirm the functionality of each LED and the cluster control circuitry.

The instrument cluster, also known as the Cab Compartment Node (CCN) continually monitors the electronic messages from the FCM to determine the proper turn signal and hazard warning indicator operation.

For proper diagnosis of the turn signal and hazard warning system, the multi-function switch, the FCM, the CCN, the CAN data bus or the electronic communication related to turn signal indicator operation a diagnostic scan tool is required. Refer to the appropriate diagnostic information.