Principles of Operation: Notes

NOTE: Whenever a network message is suspected as missing or confirmed by a missing message DTC (U-code), it is important to look for other conditions that may also be present in the Instrument Panel Cluster (IPC) and throughout the vehicle. Once a DTC sets in the IPC, it may be helpful to review the complete message list available in 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 IPC 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 illuminated, 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 IPC 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 IPC 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.
whether the module which received the input controls the output of the feature, or whether it outputs a message over the communication network to another module.
which module controls the output of the feature.