Part 2 of 2
GAUGESAll gauges receive battery current through the EMIC circuitry 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 EMIC circuitry is programmed to move 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 EMIC gauges are air core magnetic units. Two fixed electromagnetic coils are located within each gauge. These coils are wrapped at right angles to each other around a movable permanent magnet. The movable magnet is suspended within the coils on one end of a pivot shaft, while the gauge needle is attached to the other end of the shaft. One of the coils has a fixed current flowing through it to maintain a constant magnetic field strength. Current flow through the second coil changes, which causes changes in its magnetic field strength. The current flowing through the second coil is changed by the EMIC circuitry in response to messages received over the PCI data bus. The gauge needle moves as the movable permanent magnet aligns itself to the changing magnetic fields created around it by the electromagnets.
The gauges are diagnosed using the EMIC self-diagnostic actuator test. (Refer to ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). Proper testing of the PCI data bus and the electronic data bus message inputs to the EMIC that control each gauge require the use of a DRB III scan tool. Refer to the appropriate diagnostic information. Specific operation details of the operation for each gauge may be found elsewhere in this service information.
VACUUM-FLUORESCENT DISPLAYS
The two Vacuum-Fluorescent Display (VFD) units are soldered to the EMIC circuit board. Both 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 VFD units is controlled by the EMIC circuitry based upon an input from the headlamp switch and a dimming level input received from the headlamp dimmer switch. The EMIC synchronizes the illumination intensity of other VFD units with that of the units in the EMIC by sending electronic dimming level messages to other electronic modules in the vehicle over the PCI data bus.
The EMIC VFD units have several display capabilities including odometer, trip odometer, gear selector indication (PRNDL), several warning or reminder indications, and certain diagnostic information whenever the appropriate conditions exist. An odometer/trip odometer switch on the EMIC 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 center. Actuating this switch momentarily with the ignition switch in the ON position will toggle the VFD between the odometer and trip odometer modes. The word "TRIP" will also appear in blue-green text when the VFD trip odometer mode is active. Depressing the switch button for about two seconds while the VFD is in the trip odometer mode will reset the trip odometer value to zero. Holding this switch depressed while turning the ignition switch from the OFF position to the ON position will initiate the EMIC self-diagnostic actuator test. The EMIC will automatically flash the odometer or trip odometer information ON and OFF if there is a loss of PCI data bus communication. The VFD will also display various information used in several diagnostic procedures. Refer to the appropriate diagnostic information for additional details on this VFD function.
Both VFD units are diagnosed using the EMIC self-diagnostic actuator test. (Refer to ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). Proper testing of the PCI data bus and the electronic data bus message inputs to the EMIC that control some of the VFD functions require the use of a DRB III 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 these VFD units may be found elsewhere in this service information.
INDICATORS
Indicators are located in various positions within the EMIC and are all connected to the EMIC circuit board. The high beam indicator, washer fluid indicator and the turn signal indicators operate based upon hard wired inputs to the EMIC. The brake indicator is controlled by PCI data bus messages from the Controller Anti-lock Brake (CAB) as well as by a hard wired park brake switch input to the EMIC. The seatbelt indicator is controlled by the EMIC programming, PCI data bus messages from the Airbag Control Module (ACM), and a hard wired seat belt switch input to the EMIC. The security indicator is controlled by a hard wired Central Timer Module (CTM) input to the EMIC, as well as by PCI data bus messages from the Sentry Key Immobilizer Module (SKIM) if the vehicle is equipped with the optional Sentry Key Immobilizer System (SKIS). The Malfunction Indicator Lamp (MIL) is normally controlled by PCI data bus messages from the Powertrain Control Module (PCM); however, if the EMIC loses PCI data bus communication, the EMIC circuitry will automatically turn the MIL ON, and flash the odometer VFD unit ON and OFF repeatedly until PCI data bus communication is restored. The EMIC uses PCI data bus messages from the CTM, the PCM, the Transmission Control Module (TCM), the Transfer Case Control Module (TCCM), the ACM, and the CAB to control all of the remaining indicators.
The various EMIC indicators are controlled by different strategies; some operate only when the EMIC circuitry receives a battery current input on a fused ignition switch output circuit, while others will operate regardless of the ignition switch position. However, all indicators except the high beam indicator and the security indicator are completely controlled by the EMIC microprocessor based upon various hard wired and electronic message inputs. All indicators, except those located within one of the VFD units, are illuminated at a fixed intensity which is not affected by the selected illumination intensity of the EMIC general illumination lamps.
In addition, certain indicators in this instrument cluster are programmable or configurable. This feature allows the programmable indicators to be activated or deactivated with a DRB III scan tool, while the configurable indicators will be automatically enabled or disabled by the EMIC circuitry for compatibility with certain optional equipment. The only programmable indicator for this model is the upshift indicator. The cruise indicator, service 4WD indicator, door ajar indicator, liftgate ajar indicator, overdrive-off indicator, and the transmission overtemp indicator are automatically configured, either electronically or mechanically. If the EMIC is disconnected from the fused B(+) circuit for more than about 5 minutes the EMIC will forget its previous electronic configuration settings, but will learn the proper indicator configuration settings again when it is reinstalled in a vehicle.
The hard wired indicator inputs may be diagnosed using conventional diagnostic methods. However, the indicators, the EMIC circuitry and the PCI data bus electronic messages that control the indicators are diagnosed using the EMIC self-diagnostic actuator test. (Refer to ELECTRICAL/INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). Proper testing of the PCI data bus and the electronic message inputs to the EMIC that control an indicator require the use of a DRB III scan tool. Refer to the appropriate diagnostic information. Specific details of the operation for each indicator may be found elsewhere in this service information.
CLUSTER ILLUMINATION
The EMIC has several illumination lamps that are illuminated when the exterior lighting is turned ON with the headlamp switch. The illumination intensity of these lamps is adjusted by the panel lamps dimmer rheostat when the headlamp switch thumbwheel is rotated (down to dim, up to brighten). The illumination lamps receive battery current through the panel lamps dimmer rheostat and a fuse in the JB on a fused panel lamps dimmer switch signal circuit. The illumination lamps are grounded at all times.
In addition, an analog/digital (A/D) converter in the EMIC converts the analog panel lamps dimmer rheostat input from the headlamp switch to a digital dimming level signal for controlling the lighting level of the VFD units on the cluster circuit board. The EMIC also broadcasts this digital dimming information as a message over the PCI data bus for use by the Compass Mini-Trip Computer (CMTC) and the radio in synchronizing the lighting level of their VFD units with that of the EMIC VFD units. The headlamp switch thumbwheel also has a Parade Mode position to provide a parade mode. The EMIC monitors the request for this mode through a hard wired day brightness sense circuit input from the headlamp switch. In this mode, the EMIC will override the selected panel dimmer switch signal and send a message over the PCI data bus 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 parade mode has no effect on the incandescent bulb illumination intensity.
The hard wired cluster illumination lamps may be diagnosed using conventional diagnostic methods. However, proper testing of the VFD unit dimming level and the electronic dimming level messages sent by the EMIC over the PCI data bus requires the use of a DRB III scan tool. Refer to the appropriate diagnostic information.
BRAKE TRANSMISSION SHIFT INTERLOCK CONTROL
The EMIC Brake Transmission Shift Interlock (BTSI) control is only active when the automatic transmission gearshift selector lever on the steering column is in the Park position. The BTSI locks the gear selector lever in the Park position when the BTSI solenoid control coil is energized, and unlocks the lever when the control coil is de-energized. When the EMIC receives battery current on the fused ignition switch output (run-start) circuit (ignition switch is in the ON or Start positions), and either the hard wired Transmission Range Sensor (TRS) input to the EMIC or the electronic gear selector indicator messages received from the Transmission Control Module (TCM) indicate that the gear selector lever is in the Park position, the EMIC provides battery current through a high-side driver to the BTSI solenoid control coil.
The BTSI solenoid control coil is connected in series between the output of the instrument cluster and ground through the normally closed contacts of the brake lamp switch. The brake lamp switch provides the BTSI solenoid with a path to ground only when these normally closed switch contacts are closed (brake pedal is released), and de-energizes the solenoid to unlock the gear selector lever from the Park position only when the switch contacts are opened (brake pedal is depressed). However, if the EMIC senses a short or open in the TRS input or if the EMIC receives no electronic gear selector position messages from the TCM, the EMIC will automatically de-energize the BTSI solenoid to unlock the gear selector lever from the Park position.
The hard wired inputs to and outputs from the EMIC that control the BTSI solenoid may be diagnosed using conventional diagnostic methods. However, proper testing of the EMIC, the TCM, the PCI data bus, or the electronic gear selector indicator (PRNDL) messages sent by the TCM to the EMIC requires the use of a DRB III scan tool. Refer to the appropriate diagnostic information.
CHIME WARNING REQUESTS
The EMIC is programmed to request chime service from the Central Timer Module (CTM) when certain indicators are illuminated. When the programmed conditions are met, the EMIC generates an electronic chime request message and sends it over the PCI data bus to the CTM. Upon receiving the proper chime request message, the CTM activates an internal chime tone generator to provide the audible chime tone to the vehicle operator. (Refer to ELECTRICAL/CHIME/BUZZER - OPERATION). Proper testing of the EMIC, the CTM, the PCI data bus, and the electronic chime request messages sent by the EMIC to the CTM requires the use of a DRB III scan tool. Refer to the appropriate diagnostic information.
TURN SIGNAL WARNING
The EMIC provides a turn signal warning feature by monitoring the turn signal indicators and electronic vehicle speed and distance messages received from the PCM over the PCI data bus. If the EMIC determines that a turn signal is left ON for a distance greater than about 1.6 kilometers (1 mile) at a vehicle speed greater than about 24 km/h (15 mph), it will send an electronic message to the CTM requesting a continuous chime to sound until the turn signal is turned OFF or until the vehicle speed is less than 24 km/h (15 mph), whichever occurs first.
The hard wired turn signal switch inputs to the EMIC may be diagnosed using conventional diagnostic methods. However, proper testing of the EMIC, the CTM, the PCM, the PCI data bus, and the electronic messages sent by the PCM to the EMIC or from the EMIC to the CTM requires the use of a DRB III scan tool. Refer to the appropriate diagnostic information.