Principles of Operation

Instrumentation, Message Center and Warning Chimes

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

The Instrument Cluster (IC), message center and warning chimes utilize a microprocessor to control the gauge and indicator functions. Data is sent to the IC over the High Speed Controller Area Network (HS-CAN) bus lines and through hardwired circuitry from individual components. The IC uses each input to output an action to the gauges or indicators. The IC uses input messages from other modules to control the gauges, informational indicators, warning indicators, message center and warning chimes over the communication networks. If a required message is missing or invalid for less than 5 seconds, the gauge or indicator that requires the message remains at the last commanded state based upon the last known good message. For example, if the brake status message is missing for less than 5 seconds and the brake warning indicator was ON, the indicator remains in the ON state until the next good message is received. If the message remains missing or invalid for greater than 5 seconds, the IC sets a U-code DTC and the output becomes a default action for the indicator or gauge. Each indicator or gauge utilizes a different default strategy depending on the nature of the indication. Refer to the normal operation descriptions located before each individual pinpoint test for further description of the default action specific to each indicator or gauge. If the messaged input to the cluster returns at any time, the normal function of the gauge or indicator resumes.

NOTE: Whenever a network message is suspected as missing and confirmed by a missing message DTC (U-code), it is important to look for other symptoms that may also be present in the IC and throughout the vehicle. Once a DTC is set in the IC, it may be helpful to review the complete message list available in Information Bus to see what other modules also rely on the same message and run the self-test for those modules. If the message is missing from other modules, the same DTC may also be set in those modules. Confirmation of missing messages common to multiple modules may indicate that the originating module is the source of the concern or the communication network may be experiencing some problems.

It is very important to understand:

- where the input originates.
- all the information necessary in order for a feature to operate.
- which module(s) receive(s) the input or command message.
- does the module which received the input control the output of the feature, or does it output a message over the communication network to another module.
- which module controls the output of the feature.


Instrument Cluster (IC)

IC Gateway Function

The IC acts as a gateway module by receiving information in one format and transmitting it to other modules using another format. For example, the IC receives the vehicle speed data from the PCM over the HS-CAN, converts the data into a Medium Speed Controller Area Network (MS-CAN) message and sends (gateways) the message to other network modules such as the HVAC module, the Audio Control Module (ACM), and the SJB. This enables network communication between modules that do not communicate using the same network (HS-CAN or MS-CAN).

IC Configuration

The IC contains items that are configurable. All configurable items are configured at the end of the line production and only available for configuration using Programmable Module Installation (PMI) or As-Built data. Refer to Information Bus for PMI module configuration.

IC Prove-Out

The IC and other vehicle modules carry out a display prove-out to verify that all module controlled warning/indicator lamps and monitored systems are functioning correctly within the IC. When the ignition switch is cycled to the ON position with the engine off, the indicators illuminate to prove-out according the following table:






Information And Message Center

The message center is a vacuum fluorescent display, which is part of the IC. The message center electronic functions use both hardwired and controller area network (CAN) circuits to transmit and receive information.


Warning Chimes

Chime Characteristics

Each warning chime has unique characteristics that help to identify and differentiate each warning chime. The warning chimes use volume, chime frequency, length of time the chime sounds and the number of chime tones to identify which chime is sounding. The IC prioritizes the chimes according to a preset hierarchy programmed into the IC software. When more than one chime request is received by the IC, the most important chime sounds. If a lower priority chime is currently sounding, the higher priority request takes over and replaces the lower priority chime.

Safety Belt Warning Chime

The safety belt warning chime is activated when the ignition switch is in the RUN or START position and the Restraints Control Module (RCM) detects an unbuckled driver safety belt. The IC generates the chime for a duration of 6 seconds or until the safety belt is buckled.

Belt-Minder(R)

The Belt-Minder(R) feature supplements the current safety belt warning function. The Belt-Minder(R) feature is enabled after the current safety belt warning is complete. The Belt-Minder(R) reminds the driver that the driver or passenger safety belt is unbuckled by intermittently sounding a chime and illuminating the safety belt warning lamp in the IC once the vehicle speed has exceeded 5 km/h (3 mph). While activated, the Belt-Minder(R) alternates the chime and indicator from ON for 6 seconds, to OFF for 30 seconds.

NOTE: The Belt-Minder(R) is a configurable item. To configure without using a scan tool, refer to Belt-Minder(R) Deactivating/Activating Service and Repair.

The Belt-Minder(R) reminder stops when:

- The driver or passenger safety belt is buckled.
- The ignition switch is turned to the OFF or ACC position.
- Five minutes have elapsed since Belt-Minder(R) has started.

Key-In-Ignition Warning Chime

When the key-in-ignition switch closes, it sends a voltage signal to the IC, which then sounds a warning chime, provided the ignition key is in the ignition lock cylinder, the ignition switch is in the OFF position, and the driver door is open. The IC sounds a steady tone, which continues until the key is removed, the ignition switch is rotated to the RUN position, or the driver door is closed.

Air Bag Warning Chime

The air bag warning chime warns the driver that a fault has occurred in the Supplemental Restraint System (SRS) and that the air bag warning indicator lamp is not working by sounding a chime when the ignition switch is in the RUN position for more than 20 seconds. When these conditions exist, the RCM removes the ground to the IC. The IC then activates the warning chime. The warning consists of 5 sets of 5 one-second tone bursts. Each set is separated by 5 seconds of silence. The warning is repeated every 30 minutes.

Door/Trunk Ajar Warning Chime

The door/trunk ajar warning chime warns that a door, or the trunk, is not fully closed. The chime sounds when any door or the trunk becomes ajar while the ignition switch is in the RUN position.

Headlamps On Warning Chime

The headlamps on warning chime is activated when the IC receives the parking lamps ON message from the SJB, the key is out of the ignition, and the driver door is ajar. The warning consists of repeated one-half second bursts and continues to sound until the exterior lamps are turned off, the driver door is closed, or 10 minutes have elapsed, at which time the battery saver turns the exterior lamps off.

Message Center Warning Chime

The message center warning chime accompanies any initial warning message display, as well as any repeated initial warning message. As the message center is an integral part of the IC, the interaction between the message center and the chime function is also integral to the IC.

The message center switch tone sounds when any switch on the message center is pressed. The message center switches are supplied with a voltage reference signal from the IC. When a switch is pressed, it routes the signal through a specific resistor in the switch assembly and then to ground.

Performance Shift Warning Chime

The performance shift warning chime provides an audible alert to inform the driver to shift the transmission gear. The chime is configured through the message center independently of the visual performance shift indicator. The chime feature on/off status and the desired rpm for the chime to sound are configurable items. The IC uses engine data rpm sent to the IC over the HS-CAN communication lines and compares the value against the customer preset engine rpm to determine when to sound the chime. When the actual engine rpm matches the preset engine rpm, the IC sounds the chime.