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 cluster programming, a hard wired multiplex input received by the cluster 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 Totally Integrated Power Module (TIPM) 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:
The instrument cluster, also known as the Cab Compartment Node (CCN) continually monitors the multi-function switch and electronic messages from the TIPM to determine the proper turn signal and hazard warning indicator operation. For further diagnosis of the turn signal indicators or the instrument cluster circuitry that controls the indicators, (Refer to 08 - Electrical/8J - Instrument Cluster/Instrument Cluster - Diagnosis and Testing) .
For proper diagnosis of the turn signal and hazard warning system, the multi-function switch, the TIPM, the CCN, the CAN data bus or the electronic communication related to turn signal indicator operation a diagnostic scan tool is required. Perform the appropriate diagnostic procedures as needed.