Instrument Cluster - Principles of Operation

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INSTRUMENT CLUSTER - PRINCIPLES OF OPERATION

NOTE:The smart junction box (SJB) is also known as the generic electronic module (GEM).
The instrument cluster utilizes a microprocessor to control the gauge and indicator functions. Data is sent to the instrument cluster over the high speed controller area network (HS-CAN), the medium speed controller area network (MS-CAN) and through hardwired circuitry from individual components. The instrument cluster uses each input to output an action to the gauges or indicators.
NOTE:Whenever a 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 instrument cluster and throughout the vehicle. Once a DTC is set in the instrument cluster, it may be helpful to review the complete message list available in Description and Operation 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.
The instrument cluster uses input messages from other modules to control the gauges, informational indicators, and warning indicators 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 system 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 more than 5 seconds, the instrument cluster 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. see the normal operation descriptions located before each individual pinpoint test for a 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.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 Gateway Function

The instrument cluster acts as a gateway module by receiving information in one format and transmitting it to other modules using another format. For example, the instrument cluster receives the vehicle speed data from the PCM over the HS-CAN, converts the data into a MS-CAN message and sends (gateways) the message to other network modules such as the manual climate control module, the audio unit, the restraints control module (RCM) and the smart junction box (SJB). This enables network communication between modules that do not communicate using the same network (HS-CAN or the MS-CAN).

Instrument Cluster Prove-Out

The instrument cluster contains items that are configurable. While some configurable items are customer preference items, most items are configured at the end of the line production and only available for configuration using As-Built data. For additional information on As-Built data and module configuration.
NOTE:When installing a new instrument cluster it is necessary to upload the module configuration to the scan tool into the new instrument cluster. It is also necessary to carry out a parameter reset procedure whenever a new instrument cluster or PCM is installed.
The configurable customer preference item is as follows:

- Belt-Minder(R)

Instrument Cluster Prove-Out

The instrument cluster 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 instrument cluster. The instrument cluster and other modules such as the restraints control module (RCM) provide a timed prove-out while other indicators illuminate until engine start up. When the ignition switch is cycled to the ON position with the engine off, the indicators illuminate to prove-out according to the following table:





Integrated Circuit Display

The integrated circuit display is a vacuum fluorescent (VF) display that contains the odometer and trip odometer. The odometer information is transmitted from the PCM over the communication network to the instrument cluster. The instrument cluster displays the appropriate message(s)/display upon receipt of the data received.