Instrument Cluster - Operation

OPERATION

The Instrument Cluster (IC) (also known as the Common Instrument Cluster/CIC) is designed to allow the vehicle operator to monitor the conditions of many of the vehicle components and operating systems. The gauges and indicators in the IC provide valuable information about the various standard and optional power trains, fuel and emissions systems, cooling systems, lighting systems, safety systems and many other convenience items. The IC is installed in the instrument panel so that the operator of the vehicle can view all of these monitors easily, yet still allow relative ease of access for service.

The microprocessor-based IC hardware and software uses various inputs to control the gauges and indicators visible on the face of the cluster. Some of these inputs are hard wired, but most are in the form of electronic messages that are transmitted by other electronic modules over the Controller Area Network (CAN) data bus and the Local Interface Network (LIN) data bus. Communication - Operation.

The IC microprocessor smooths the input data using algorithms to provide gauge readings that are accurate, stable and responsive to operating conditions. These algorithms are designed to provide gauge readings during normal operation that are consistent with customer expectations. However, when abnormal conditions exist such as high coolant temperature, the algorithm can drive the gauge pointer to an extreme position and the microprocessor can sound a chime warning to provide distinct visual and audible indications of a problem to the vehicle operator. The IC may also produce audible warnings for other electronic modules in the vehicle based upon electronic chime request messages received over the CAN data bus. Each audible warning is intended to provide the vehicle operator with an audible alert to supplement a visual indication.

The IC circuitry operates on battery current received through a fused B(+) fuse on a non-switched fused B(+) circuit, and on battery current received through a fused ignition switch output (run-start) fuse on a fused ignition switch output (run-start) circuit. This arrangement allows the IC to provide some features regardless of the ignition switch position, while other features will operate only with the ignition switch in the ON or START positions. The circuitry is grounded through a ground circuit of the instrument panel wire harness.

The IC also has a self-diagnostic test capability that tests each of the CAN bus message-controlled functions of the cluster. This test illuminates the appropriate indicators, positions the gauge needles at several predetermined calibration points across the gauge faces and illuminates all segments of the Electronic Vehicle Information Center (EVIC). The EVIC will display the hardware/software version and the CAN Vehicle Maintenance Monitor (VMM) used in the IC within the Thin Film Transistor (TFT) display unit. Testing and Inspection.

CLUSTER ILLUMINATION

Instrument cluster illumination is supplied by several Light Emitting Diode (LED) units controlled by the IC. The illumination intensity of these LED units can be adjusted only when the exterior lighting is turned ON by rotating the panel dimmer switch thumbwheel (down to dim, up to brighten) of the dimmer module to one of five available minor detent positions. The illumination intensity of the LED units is controlled by the IC circuitry based upon electronic dimming level messages received from the Body Control Module (BCM) (also known as the Common Body Controller/CBC) over the Controller Area Network (CAN) data bus. The BCM monitors an input from the headlamp switch and a dimming level input received from the panel dimmer switch of the dimmer module.

The hard-wired headlamp switch and dimmer module inputs to the BCM may be diagnosed using conventional diagnostic methods. However, proper testing of the electronic communication and processing of the IC and the electronic dimming level messages sent by the BCM over the CAN data bus requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.

THIN FILM TRANSISTOR DISPLAY

The Thin Film Transistor (TFT) display unit is soldered to the IC electronic circuit board. With the ignition switch in the OFF or ACCESSORY positions, the TFT display is activated when the driver door is opened (Rental Car mode) and deactivated when the driver door is closed. Otherwise, the display units are active when the ignition switch is in the ON or START positions, and inactive when the ignition switch is in the OFF or ACCESSORY positions.

The illumination intensity of the TFT unit is controlled by the IC circuitry based upon electronic dimming level messages received from the Body Control Module (BCM) (also known as the Common Body Controller/CBC) over the Controller Area Network (CAN) data bus. The BCM monitors an input from the headlamp switch and a dimming level input received from the panel dimmer switch of the dimmer module. The BCM synchronizes the illumination intensity of other display units with that of the unit in the IC by sending electronic dimming level messages to other electronic modules in the vehicle over the CAN data bus.

The IC TFT display unit has several display capabilities. The TFT unit displays odometer, trip odometer, gear selector indication (PRNDL) for models with an automatic transmission, both static and animated graphics, several warning or reminder indications and various diagnostic information when certain fault conditions exist. Steering wheel mounted switches are used to control some of the display modes of the TFT. Electronic Vehicle Information Center - Operation for more information.

The TFT display unit is diagnosed using the IC self-diagnostic actuator test. Testing and Inspection. Proper testing of the CAN data bus and the electronic data bus message inputs to the IC that control some of the TFT display functions requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information. Specific operation details for the odometer, the trip odometer, the gear selector indicator and the various warning and reminder indicator functions of the TFT display unit may be found elsewhere in this service information.