Turn Signal Indicator

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 Panel Cluster (IPC) electronic circuit board based upon IPC programming, a hard wired multiplex input received by the IPC from the turn signal and hazard warning switch circuitry of the multi-function switch on the turn/hazard switch mux circuit, and electronic messages received from the Body Control Module (BCM) over the Controller Area Network (CAN) data bus.

Each turn signal indicator Light Emitting Diode (LED) is completely controlled by the BCM logic circuit, and that logic will allow this indicator to operate whenever the IPC 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 IPC transistor. The IPC will turn ON the turn signal indicators for the following reasons:

• Turn Signal-On Input  - Each time the IPC detects a turn signal-ON input from the turn signal switch circuitry of the multi-function switch on the turn/hazard switch mux circuit, it 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 IPC 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 IPC 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 IPC receives a turn signal-OFF input from the multi-function switch, or until the ignition switch is turned to the OFF position, whichever occurs first.
• Hazard Warning-On Input  - Each time the IPC detects a hazard warning-ON input from the hazard warning switch circuitry of the multi-function switch on the turn/hazard switch mux circuit, it sends the appropriate electronic hazard 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 each of the right and left turn signal lamps. The BCM also sends the appropriate electronic messages back to the IPC 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 IPC 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 input from the multi-function switch.
• Lamp Out Mode  - If the BCM 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 IPC 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.

The IPC continually monitors the multi-function switch and electronic messages from the BCM to determine the proper turn signal and hazard warning indicator operation. For further diagnosis of the turn signal indicators or the IPC circuitry that controls the indicators. Refer to DIAGNOSIS AND TESTING .