Part 1

OPERATION

The microprocessor-based Cab Compartment Node (CCN) hardware and software uses various inputs to control the gauges and indicators visible on the face of the instrument cluster. Some of these inputs are hardwired. 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 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 also produces audible warnings for other electronic modules in the vehicle based upon electronic tone request messages received over the CAN data bus. Each audible warning provides 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 operate only with the ignition switch in the ON or START positions. The CCN circuitry is grounded through a ground circuit of the instrument panel wire harness.

The CCN also has a self-diagnostic actuator test capability Testing and Inspection , which tests each of the CAN bus message-controlled functions of the cluster. It does this 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 and gear selector indicator Vacuum-Fluorescent Display (VFD) units.

GAUGES

All gauges receive battery current through the CCN circuitry only 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 moves all of the gauge needles back to the low end of their respective scales. Therefore, the gauges do not accurately indicate any vehicle condition unless the ignition switch is in the ON or START positions.

All of the 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 at "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.

ENGINE COOLANT TEMPERATURE GAUGE

The instrument cluster circuit board controls the engine coolant temperature gauge based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the CAN data bus.

The engine coolant temperature gauge is a stepper motor gauge that receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or START positions. The cluster moves the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The instrument cluster circuitry controls the gauge needle position and provides the following features:

- Engine Temperature Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is between the low end of normal [about 49° C (120° F)] and the high end of normal [about 124° C (255° F)], the gauge needle moves to the actual relative temperature position on the gauge scale.
- Engine Temperature Low Message - Each time the cluster receives a message from the PCM indicating the engine coolant temperature is below the low end of normal [about 49° C (120° F)], the gauge needle holds at the "C" increment at the low end of the gauge scale. The gauge needle remains at the low end of the gauge scale until either the cluster receives a message from the PCM, indicating that the engine temperature is above about 54° C (130° F), or until the ignition switch is turned to the OFF position, whichever occurs first.
- Engine Temperature High Message - Each time the cluster receives a message from the PCM, indicating the engine coolant temperature is above about 124° C (255° F), the gauge needle moves into the red zone on the gauge scale, the engine temperature indicator illuminates, and a single chime tone sounds. The gauge needle remains in the red zone and the engine temperature indicator remains illuminated until either the cluster receives a message from the PCM, indicating that the engine temperature is below about 124° C (255° F), or until the ignition switch is turned to the OFF position, whichever occurs first. The chime tone feature repeats during the same ignition cycle only if the engine temperature indicator is cycled off and then on again by the appropriate engine temperature messages from the PCM.
- Communication Error - If the cluster fails to receive an engine temperature message, it holds the gauge needle at the last indication for about five seconds, or until the ignition switch is turned to the OFF position, whichever occurs first. After five seconds, the cluster moves the gauge needle to the low end of the gauge scale.
- Self Test - Each time the cluster is put through the self test, the engine coolant temperature gauge needle sweeps to several calibration points on the gauge scale, in a prescribed sequence, in order to confirm the functionality of the gauge and the cluster control circuitry.

The PCM continually monitors the engine coolant temperature sensor to determine the engine operating temperature. The PCM then sends the proper engine coolant temperature messages to the instrument cluster. For further diagnosis of the engine coolant temperature gauge or the instrument cluster circuitry that controls the gauge, Testing and Inspection. If the instrument cluster illuminates the engine temperature indicator due to a high engine temperature gauge reading, it may indicate that the engine or the engine cooling system requires service. The engine coolant temperature gauge is serviced as a unit with the instrument cluster.

FUEL GAUGE

The fuel gauge indicates the level of fuel in the fuel tank to the vehicle operator. This gauge is controlled by the instrument cluster circuit board based upon cluster programming and a hardwired input received by the cluster from the fuel level sending unit on the fuel pump module in the fuel tank.

The fuel gauge is a stepper motor magnetic unit. It receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output ( RUN-START ) circuit whenever the ignition switch is in the ON or START positions. The cluster moves the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The instrument cluster circuitry controls the gauge needle position and provides the following features:

- Fuel Level Sending Unit Input - The cluster provides a constant current source to the fuel level sending unit and monitors a return input on a fuel level sense circuit. The resistance through the fuel level sending unit increases as the fuel level falls and decreases as the fuel level rises causing changes in the sense input voltage. The cluster programming applies an algorithm to calculate the proper fuel gauge needle position, based upon the fuel level sense input, then moves the gauge needle to the proper relative position on the gauge scale. This algorithm dampens gauge needle movement against the negative effect that fuel sloshing within the fuel tank can have on accurate inputs from the fuel tank sending unit to the cluster.
- Less Than Ten Percent Tank Full Input - The LC is equipped with a 19 gallon saddle-type fuel tank with a sending unit on each side. The sending units are hardwired to the CCN. The CCN averages the sending unit voltages and provides the proper gauge positioning. the CCN responds each time the fuel level sense input to the cluster indicates the fuel tank is about ten percent full or less, for ten consecutive seconds, and the vehicle speed is zero; or for sixty consecutive seconds, and the vehicle speed is greater than zero. The gauge needle moves to about the one-eighth graduation on the gauge scale, the low fuel indicator illuminates, and a single chime tone sounds. The low fuel indicator remains illuminated until the fuel level sense input indicates the fuel tank is greater than about thirteen percent full, for ten consecutive seconds, and the vehicle speed is zero; or for sixty consecutive seconds, and the vehicle speed is greater than zero, or until the ignition switch is turned to the OFF position, whichever occurs first. The chime tone feature will only repeat during the same ignition cycle if the low fuel indicator is cycled off and then on again by the appropriate inputs from the fuel level sending unit.
- Less Than Empty Stop Input - Each time the fuel level sense input to the cluster indicates the fuel level in the fuel tank is less than empty, the gauge needle moves to the low end of the gauge scale and the low fuel indicator illuminates immediately. This input indicates the fuel level sense input to the cluster is a short circuit.
- More Than Full Stop Input - Each time the fuel level sense input indicates the fuel level in the fuel tank is more than the Full gauge needle stop position, and the gauge needle moves to the low end of the gauge scale, the low fuel indicator illuminates immediately. This input indicates the fuel level sense input to the cluster is an open circuit.
- Self Test - Each time the cluster is put through the self test, the fuel gauge needle sweeps to several calibration points on the gauge scale in a prescribed sequence to confirm the functionality of the gauge and the cluster control circuitry.

The instrument cluster continually monitors the fuel tank sending unit to determine the level of fuel in the fuel tank. The cluster then sends the proper fuel level messages to other electronic modules in the vehicle over the CAN data bus. For further diagnosis of the fuel gauge or the instrument cluster circuitry that controls the gauge, Testing and Inspection. The fuel gauge is serviced as a unit with the instrument cluster.

SPEEDOMETER

The speedometer indicates the vehicle speed to the operator. The instrument cluster circuit board controls the speedometer based upon cluster programming and electronic messages received by the cluster from the Front Control Module (FCM). The FCM receives the vehicle speed information across the CAN data bus by either the PCM, the Electronic Stability Program (ESP) module or the Anti-lock Brake System (ABS) module.

The instrument cluster circuitry controls the gauge needle position and provides the following features:

- Vehicle Speed Message - Each time the cluster receives a vehicle speed message from the FCM, it calculates the correct vehicle speed reading and positions the gauge needle at that relative speed position on the gauge scale. The cluster receives a new vehicle speed message and repositions the gauge pointer accordingly about every 50 milliseconds. The gauge needle is continually positioned at the relative vehicle speed position on the gauge scale until the vehicle stops moving, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Communication Error - If the cluster fails to receive a speedometer message, it holds the gauge needle at the last indication for about three seconds, or until the ignition switch is turned to the Off position, whichever occurs first. After three seconds, the gauge needle returns to the left end of the gauge scale.
- Self Test - Each time the cluster is put through the self test, the speedometer needle sweeps to several calibration points on the gauge scale in a prescribed sequence to confirm the functionality of the gauge and the cluster control circuitry.

The PCM continually monitors the vehicle speed sensor to determine the vehicle road speed. The PCM sends the proper vehicle speed messages to the instrument cluster. For further diagnosis of the speedometer or the instrument cluster circuitry that controls the gauge, Testing and Inspection. The speedometer is serviced as a unit with the instrument cluster.

TACHOMETER

The tachometer indicates engine speed to the vehicle operator. The instrument cluster circuit board controls the tachometer based upon cluster programming and electronic messages received by the cluster from the PCM over the CAN data bus.

The tachometer is a stepper motor magnetic unit. It receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output ( RUN-START ) circuit whenever the ignition switch is in the ON or START positions. The cluster moves the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The instrument cluster circuitry controls the gauge needle position and provides the following features:

- Engine Speed Message - Each time the cluster receives an engine speed message from the PCM it calculates the correct engine speed reading and positions the gauge needle at that relative speed position on the gauge scale. The cluster receives a new engine speed message and repositions the gauge pointer accordingly about every 50 milliseconds. The gauge needle is continually repositioned at the relative engine speed position on the gauge scale until the engine stops running, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Communication Error - If the cluster fails to receive an engine speed message, it holds the gauge needle at the last indication for about three seconds, or until the ignition switch is turned to the OFF position, whichever occurs first. After three seconds, the gauge needle returns to the left end of the gauge scale.
- Self Test - Each time the cluster is put through the self test, the tachometer needle sweeps to several calibration points on the gauge scale in a prescribed sequence to confirm the functionality of the gauge and the cluster control circuitry.

The PCM continually monitors the crankshaft position sensor to determine the engine speed. The PCM sends the proper engine speed messages to the instrument cluster. For further diagnosis of the tachometer or the instrument cluster circuitry that controls the gauge, Testing and Inspection. The tachometer is serviced as a unit with the instrument cluster.

The gauges are diagnosed using the CCN self-diagnostic actuator test Testing and Inspection. Proper testing of the CAN data bus, and the electronic data bus message inputs to the CCN that control each gauge, require the use of a diagnostic scan tool. Go to the appropriate diagnostic information.

VACUUM-FLUORESCENT DISPLAYS

The Vacuum-Fluorescent Display (VFD) units are soldered to the CCN electronic circuit board. With the ignition switch in the OFF position, the odometer display activates when the driver door opens (Rental Car mode) and deactivates when the driver door closes. Otherwise, both display units are active when the ignition switch is in the ACC or START positions and inactive when the ignition switch is in the OFF position

The CCN circuitry controls the illumination intensity of the VFD units 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 units in the CCN by sending electronic dimming level messages to other electronic modules in the vehicle over the CAN data bus.

While in the odometer mode with the ignition switch in the ON position and the engine not running, pressing the odometer/trip odometer switch for about six seconds displays the engine hours information. Pressing and holding the switch while turning the ignition switch from the OFF position to the ON position initiates the CCN self-diagnostic actuator test. Refer to the instrument cluster diagnosis and testing service information for additional details on this cluster function. Testing and Inspection The CCN microprocessor remembers the active display mode when the ignition switch is turned to the OFF position, and returns to that mode when the ignition switch is turned ON again.

The VFD units are diagnosed using the CCN self-diagnostic actuator 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.

TRANSMISSION RANGE INDICATOR

The electronic transmission range indicator indicates to the vehicle operator the transmission gear that has been selected with the automatic transmission gear selector lever. The instrument cluster circuit board controls this indicator based upon cluster programming and electronic messages received from the PCM over the CAN data bus.

The transmission range indicator information is displayed by a dedicated VFD unit soldered onto the instrument cluster electronic circuit board. The VFD does not display the transmission range indicator information after the ignition switch is turned to the OFF position. The instrument cluster circuitry operates the transmission range indicator VFD to provide the following features:

- Selected Gear Message - Each time the cluster receives a selected gear message from the PCM, a box illuminates around the appropriate character in the gear selector indicator VFD. The box remains illuminated until the cluster receives a different selected gear message, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Communication Error - If the cluster fails to receive a selected gear message from the PCM within three seconds, the instrument cluster circuitry displays all gear selector positions boxed (selected) until a valid selected gear message is received, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Self Test - Each time the cluster is put through the self test, the gear selector indicator VFD displays all of its characters at once, then steps through each character segment individually during the VFD portion of the test to confirm the functionality of the VFD and the cluster control circuitry.

The PCM continually monitors a hardwired multiplex input from the Transmission Range Sensor (TRS), then sends the proper selected gear messages to the instrument cluster. For further diagnosis of the transmission range indicator or the instrument cluster circuitry that controls this function, Testing and Inspection. The transmission range indicator is serviced with the instrument cluster.

INDICATORS

Indicators are located in various positions within the CCN and are all connected to the CCN electronic circuit board. 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 blue/green indicators located within the VFD unit dim accordingly with the instrument panel dimming. The red indicators within the VFD are at a fixed intensity.

ABS INDICATOR





The ABS indicator indicates to the vehicle operator that the ABS system is faulty or inoperative. The low side driver on the instrument cluster circuit board controls this indicator based upon cluster programming and electronic messages received by the cluster from the Controller Antilock Brake (CAB) over the CAN data bus.

The ABS indicator LED is completely controlled by the instrument cluster logic circuit. That logic allows this indicator to operate only when the instrument cluster receives a battery current input on the fused ignition switch output (run-start) circuit. Therefore, the LED is always off when the ignition switch is in any position except ON or START. The LED illuminates only when it is provided a path to ground by the instrument cluster transistor. The instrument cluster turns on the ABS indicator for the following reasons:

- Bulb Test - Each time the ignition switch is turned to the ON position the ABS indicator illuminates for about three seconds as a bulb test. The entire bulb test is a function of the CAB.
- ABS Lamp-On Message - Each time the cluster receives a lamp-on message from the CAB, the ABS indicator will be illuminates. The indicator remains illuminated until the cluster receives a lamp-off message from the CAB, or until the ignition switch is turned to the OFF position, whichever occurs first.
- Communication Error - If the cluster receives no lamp-on or lamp-off message from the CAB for five consecutive message cycles, the ABS indicator illuminates. The indicator remains illuminated until the cluster receives a valid message from the CAB, or until the ignition switch is turned to the OFF position, whichever occurs first.
- self Test - Each time the instrument cluster is put through the self test, the ABS indicator turns on and off during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.
- ABS Diagnostic Test - The ABS indicator blinks on and off by lamp-on and lamp-off messages from the CAB during the ABS diagnostic tests.

The CAB continually monitors the ABS circuits and sensors to determine if the system is in good operating condition. The CAB then sends the proper lamp-on or lamp-off message to the instrument cluster. If the CAB sends a lamp-on message after the bulb test, the CAB has detected a system malfunction and/or the ABS system is inoperative. The CAB stores a Diagnostic Trouble Code (DTC) for any malfunction it detects.