Instrument Cluster - Operation

OPERATION

The instrument cluster includes the hardware and software necessary to serve as the electronic body control module and is sometimes referred to as the Cab Compartment Node or (CCN). The following information deals primarily with the instrument cluster functions of this unit. Additional details of the electronic body control functions of this unit may be found within the service information for the system or component that the CCN controls. For example: Additional details of the audible warning functions of the CCN are found within the Chime/Buzzer service information.

The CCN 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 CCN provide valuable information about the various standard and optional powertrains, fuel and emissions systems, cooling systems, lighting systems, safety systems and many other convenience items. The CCN is installed in the instrument panel so that all of these monitors can be easily viewed by the vehicle operator when driving, while still allowing relative ease of access for service.

The microprocessor-based CCN 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 Communication - Operation.

The CCN 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 through the on-board audible tone transducer to provide distinct visual and audible indications of a problem to the vehicle operator. The CCN may also produce audible warnings for other electronic modules in the vehicle based upon electronic tone 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 CCN 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 CCN 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 CCN circuitry is grounded through a ground circuit and take out of the instrument panel wire harness with an eyelet terminal connector that is secured by a ground screw to a ground location on the instrument panel structural support.

The CCN also has a self-diagnostic test capability, which will test each of the CAN bus message-controlled functions of the cluster by lighting the appropriate indicators, positioning the gauge needles at several predetermined calibration points across the gauge faces, and illuminating all segments of the odometer/trip odometer/gear selector indicator Liquid Crystal Display (LCD) Display unit Component Tests and General Diagnostics.

LIQUID CRYSTAL DISPLAY

The Liquid Crystal Display (LCD) unit is attached to the CCN electronic circuit board. With the ignition switch in the OFF or ACCESSORY positions, the odometer display is activated when the driver door is opened (Rental Car mode) and is deactivated when the driver door is closed. Otherwise, the display unit is 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 LCD unit is controlled by the CCN circuitry based upon an input from the headlamp switch and a dimming level input received from the panel dimmer switch. The CCN synchronizes the illumination intensity of other LCD units with that of the unit in the CCN by sending electronic dimming level messages to other electronic modules in the vehicle over the CAN data bus.

The instrument cluster LCD unit has several display capabilities including odometer, trip odometer, engine hours, fuel saver mode notification, gear selector indication (PRNDL) for vehicles with an automatic transmission, warning or reminder indications, as well as various diagnostic messages when certain fault conditions exist. An odometer/trip odometer switch on the CCN circuit board is used to control some of the display modes. This switch is actuated manually by depressing the odometer/trip odometer switch button that extends through the lower edge of the cluster lens, just left of the tachometer. Actuating this switch momentarily with the ignition switch in the ON position will toggle the LCD between the odometer and trip odometer modes. Depressing the switch button for about two seconds while the LCD is in the trip odometer mode will reset the trip odometer value to zero.

While in the odometer mode with the ignition switch in the ON position and the engine not running, depressing the odometer/trip odometer switch for about six seconds will display the engine hours information on vehicle not equipped with an EVIC. Holding this switch depressed while turning the ignition switch from the OFF position to the ON position will initiate the CCN self-diagnostic test Component Tests and General Diagnostics for additional details on this cluster function. The CCN microprocessor remembers which display mode is active when the ignition switch is turned to the OFF position, and returns the LCD display to that mode when the ignition switch is turned ON again.

The LCD unit is diagnosed using the CCN self-diagnostic test Component Tests and General Diagnostics. Proper testing of the CAN data bus and the electronic data bus message inputs to the CCN that control some of the LCD 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 LCD unit may be found elsewhere in this service information.

CLUSTER ILLUMINATION

The CCN has several illumination lamps that are illuminated whenever the ignition is turned to the ON position. The illumination intensity of these lamps is adjusted when the interior lighting thumbwheel on the headlamp switch is rotated (down to dim, up to brighten) to one of the available minor detent positions. The CCN monitors a resistor multiplexed input from the headlamp switch on a dimmer input circuit. In response to that input, the CCN electronic circuitry converts a fused 12-volt input it receives on a hardwired panel lamps dimmer switch signal circuit into a 12-volt Pulse Width Modulated (PWM) output.

The CCN uses this PWM output to control the illumination intensity of the cluster illumination lamps and the LCD unit on the CCN circuit board, then provides a synchronized PWM output on various hard wired fused panel lamps dimmer switch signal circuits to control and synchronize the illumination intensity of other incandescent illumination lamps in the vehicle. The CCN also transmits electronic dimming level messages over the CAN data bus to other electronic modules in the vehicle to control and synchronize the illumination intensity of their LCD units to that of the CCN LCD unit.

In addition, the thumbwheel on the headlamp switch has a PARADE mode position to provide a PARADE (or funeral) mode. The CCN monitors the request for this mode from the headlamp switch, then transmits an electronic dimming level message to illuminate all LCD units in the vehicle at full (daytime) intensity for easier visibility when driving in daylight with the exterior lighting turned ON.

The hard wired headlamp switch and panel lamps dimmer inputs to and outputs from the CCN may be diagnosed using conventional diagnostic tools and procedures. However, proper testing of the PWM processing of the CCN and the electronic dimming level messages sent by the CCN over the CAN data bus requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.