Instrument Cluster - Operation

OPERATION

The instrument cluster, also known as the Cab Compartment Node (CCN) has hardware and software that uses various inputs to control the gauges and indicators visible on the face of the cluster. Some of these inputs are hardwired, but most are in the form of electronic messages 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 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 non-switched fused B(+) circuit, and on battery current received through 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 operate only with the ignition switch in the ON or START positions. The CCN circuitry is grounded through a ground circuit located on the instrument panel structural support.

The CCN also has a self-diagnostic actuator test capability, which tests 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 Vacuum Fluorescent Display (VFD) unit. Testing and Inspection.

GAUGES

The gauges receive battery current through the CCN circuitry and only indicate vehicle conditions when the ignition switch is in the ON or START positions. With the ignition switch in the OFF position, battery current is not supplied to any gauges and the CCN circuitry is programmed to move all of the gauge needles back to the low end of their respective scales.

All CCN gauges are driven by stepper motors. Multiple toothed electromagnets around a central gear-shaped piece of iron are located within each gauge. The electromagnets are energized by the CCN circuitry in response to messages received over the CAN data bus. To make the motor shaft turn, one electromagnet is given power, which makes the gears teeth magnetically attract to the electromagnets. As the second electromagnet is turned on, the first is turned off and the gear rotates to align to the energized magnet and the process is repeated. Each of those slight rotations is called a "step", this allows the motor to be turned to precise angles. The gauge needle moves as the magnets align to the changing magnetic fields created around it by the electromagnets.

Self-Test - To confirm the functionality of the gauges and the cluster control circuitry, the cluster is put through a self-test. The gauge needles are swept to several calibration points on the gauge scales in a prescribed sequence. For further diagnosis of the tachometer or the instrument cluster circuitry that controls the gauge, Testing and Inspection

VACUUM-FLUORESCENT DISPLAY

The Vacuum-Fluorescent Display (VFD) unit is soldered to the CCN circuit board. With the ignition switch in the OFF or ACC. 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 ACC. positions.

The illumination intensity of the VFD 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 VFD 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 clusters VFD unit has several display capabilities, including odometer, trip odometer, engine hours, gear selector indication (PRNDL), several warning or reminder indications and various diagnostic information 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 pressing the odometer/trip odometer switch button that extends through the lower edge of the cluster lens just left of the minor gauge set. Momentarily actuating this switch with the ignition switch in the ON position toggles the VFD between the odometer and trip odometer modes. Pressing the switch button for about two seconds while the VFD is in the trip odometer mode resets the trip odometer value to zero.

While in the odometer mode, with the ignition switch in the ON position and the engine not running, press the odometer/trip odometer switch for about six seconds displays the engine hours information. Holding this switch pressed while turning the ignition switch from the OFF to the ON position initiates the CCN diagnostic self-test. Testing and Inspection. The CCN microprocessor remembers which display mode is active when the ignition switch is turned to the OFF position and returns the display to that mode when the ignition switch is turned on again.

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

INDICATORS

Indicators are located in various positions within the instrument cluster and are all connected to the CCN electronic circuit board. The door ajar indicator, gate ajar indicator, high beam indicator and the turn signal indicators operate based upon hardwired inputs to the CCN. The brake indicator is controlled by CAN data bus messages from the Controller Antilock Brake (CAB), as well as by hardwired park brake switch inputs to the CCN. The seatbelt indicator is controlled by the CCN programming, CAN data bus messages from the Occupant Restraint Controller (ORC), and a hardwired seat belt switch input to the CCN. The Malfunction Indicator Lamp (MIL) is normally controlled by CAN data bus messages from the Powertrain Control module (PCM). However, if the CCN loses CAN data bus communication, the CCN circuitry automatically turns the MIL on until CAN data bus communication is restored. The CCN uses CAN data bus messages from the Front Control Module (FCM), the PCM, the ORC, the CAB, and the Sentry Key REmote Entry Module (SKREEM) to control all of the remaining indicators.

The various CCN indicators are controlled by different strategies; some receive fused ignition switch output from the CCN circuitry and have a switched ground, while others are grounded through the CCN circuitry and have a switched battery feed. However, all indicators are completely controlled by the CCN microprocessor based upon various hardwired and electronic message inputs. The cruise, 4WD, 4WD low and tow/haul indicators and those located within the VFD unit are dimmable. All other indicators are illuminated at a fixed intensity, which is not affected by the selected illumination intensity of the CCN general illumination lamp. The illumination intensity of the dimmable indicators is synchronized with that of the general illumination lamp.

In addition, certain indicators in this instrument cluster are automatically or self-configured. This feature allows the configurable indicators to be enabled by the CCN circuitry for compatibility with certain optional equipment. The CCN defaults for the Anti lock Brake system (ABS) indicator and airbag indicator are enabled, and these configuration settings must be programmatically disabled in the CCN using a diagnostic scan tool for vehicles that do not have this equipment. The automatically or self-configured indicators remain latent at all times and are active only when the CCN receives the appropriate CAN bus message inputs for that optional system or equipment.

CLUSTER ILLUMINATION

The CCN has a single electro-luminescent lamp that provides cluster back lighting whenever the exterior lighting is turned ON. The illumination intensity of this lamp is adjusted when the interior lighting thumbwheel on the headlamp switch is rotated to one of six available minor detent positions (down to dim, up to brighten). 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 electro-luminescent cluster illumination lamp and the VFD unit on the CCN circuit board, then provides a synchronized PWM output on various hardwired 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 VFD units to that of the CCN VFD 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 VFD units in the vehicle at full (daytime) intensity for easier visibility when driving in daylight with the exterior lighting turned ON.

The electro-luminescent lamp unit consists of layers of phosphor, carbon, indium tin oxide, and dielectric applied by a silk-screen process between two polyester membranes and includes a short pigtail wire and connector. The lamp pigtail wire is connected to a connector receptacle on the CCN circuit board. The CCN powers this lamp with an Alternating Current (AC) rated at 80 volts rms (root mean squared) and 415 Hertz produced by a transformer on the circuit board, which excites the phosphor particles causing them to luminesce.

The hardwired 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.