Principles of Operation

PRINCIPLES OF OPERATION

NOTE: The smart junction box (SJB) is also known as the generic electronic module (GEM).

The base and message center instrument clusters are configurable, electronic clusters that contain a microprocessor, gauges, indicator lamps, and internal circuitry. Data is sent to the instrument cluster (IC) 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 (IC) uses each input to output an action to the gauges or indicators.

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) Gateway Function
The instrument cluster (IC) 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 (IC) 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 heating ventilation air conditioning (HVAC) module, the audio control module (ACM), the parking aid module, the restraints control module (RCM) and the SJB. This enables network communication between modules that do not communicate using the same network (HS-CAN or the MS-CAN).

Instrument Cluster (IC) Network Messages

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 instrument cluster (IC) and throughout the vehicle. Once a DTC is set in the instrument cluster (IC), it may be helpful to review the complete message list available in Information Bus (Module Communications Network) 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 (IC) 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 (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 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.

Instrument Cluster (IC) Configuration
The instrument cluster (IC) 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 are only available for configuration using programmable module installation (PMI) procedures. Refer to Information Bus (Module Communications Network) for additional information on the PMI procedure.

The Belt-Minder(R) is the only configurable customer preference item.

Instrument Cluster (IC) Prove-Out
The instrument cluster (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 instrument cluster (IC). The instrument cluster (IC) 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: