Hazard Warning Switch: Description and Operation
The hazard switch features a push-push type latching push button. The hazard switch receives a clean ground on one terminal from the
ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) Whenever the hazard switch is in its latched and
lowered position, the hazard warning system is selected and the upper instrument panel switch pod circuitry sends a hard wired output to the Front
Control Module (FCM).
When the FCM receives a hazard switch input it then controls hazard warning system operation and flash rate by controlling battery voltage outputs
through high side drivers on the right and left turn signal feed circuits. The FCM also sends the appropriate electronic messages back to the EMIC to
control the illumination and 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 EMIC electronic circuit board that emulates the sound emitted by a conventional hazard warning flasher. The EMIC then sends messages back
to the switch pod over the Local Interface Network (LIN) data bus to control the illumination of the hazard switch push button.
The hazard switch as well as the hard wired inputs and outputs of the switch may be diagnosed using conventional diagnostic tools and procedures. Refer
to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the electronic controls
and communication between other modules and devices that provide some features of the hazard switch or the hazard warning system. The most reliable,
efficient, and accurate means to diagnose the hazard switch or the electronic controls and communication related to hazard warning system operation
requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.