Operation

OPERATION

The no fuse indicator gives an indication to the vehicle operator when the Ignition Off Draw (IOD) fuse is ineffective or is not installed. This indicator is controlled by the instrument cluster logic circuit based upon cluster programming and electronic messages received over the Controller Area Network (CAN) data bus from the Front Control Module (FCM).

The no fuse indicator function of the odometer Vacuum Fluorescent Display (VFD) unit is completely controlled by the instrument cluster logic circuit, and that logic will only allow this indicator to operate when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the odometer VFD no fuse indication will always be OFF when the ignition switch is in any position except ON or START. The instrument cluster will turn ON the no fuse indicator for the following reasons:

- No Fuse Indicator Lamp-On Message - Each time the ignition switch is turned to the ON position and the cluster receives an electronic no fuse indicator lamp-ON message from the FCM indicating that the IOD fuse is missing or ineffective, the no fuse indicator will be illuminated. The indicator remains illuminated for about three seconds, until the IOD fuse is installed, until the trip odometer reset switch button is depressed or until the ignition switch is turned to the OFF position, whichever occurs first.

The FCM continually monitors the IOD circuit to determine the status of the IOD fuse, then sends the proper lamp-ON or lamp-OFF message to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) over the CAN data bus.

For proper diagnosis of the no fuse indicator, the FCM, the EMIC, the CAN data bus or the electronic communication related to no fuse indicator operation a diagnostic scan tool is required.