Networked Input Messages and Default States

The IPC 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 a programmed length of time, the gauge or indicator that requires the message remains at the last commanded state based upon the last message received.

For example, if the engine oil pressure network message is missing for less than 2 seconds and the low oil pressure indicator was on, the indicator remains in the on state until the next network message is received. Again, using the time criteria, if the network message remains missing or invalid for more than 2 seconds, the IPC sets a U-code DTC and the IPC output becomes a default action for the indicator or gauge. The indicator may default on-off or a gauge may default to the rest position.

Each indicator or gauge utilizes a different default strategy depending on the nature of the indication. Refer to the diagnostic overview descriptions located before each individual pinpoint test for further description of the default action specific to each indicator or gauge. If the missing messaged input to the IPC returns at any time, the normal function of the gauge, indicator or message center display 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 IPC and throughout the vehicle. Once a DTC sets in the IPC, it may be helpful to review the complete message list. Refer to MODULE COMMUNICATIONS NETWORK CAN, Multiplex Messages Description and Operation, to determine which 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 the originating module is the source of the concern or the communication network may be faulted.

It is very important to understand:

where the input originates.
all the information necessary for a feature to operate.
which module(s) receive(s) the input or command message.
which module controls the output of the feature.
whether the module that receives the input controls the output of the feature, or whether it outputs a message over the communication network to another module.