DTC U1001-U1254: Loss Of XXX Communication: Description

Modules connected to class 2 serial data line monitor serial data communications during normal vehicle operation. Operating information and commands are exchanged between modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State Of Health (SOH) monitoring (node alive messages).

Once an identification number is learned by a module, it will monitor for that module's node alive message. Each module on the class 2 serial data line which is powered and performing functions that require detection of a communications malfunction is required to send a node alive message every 2 seconds.

When no message is detected by from a learned identification number for 5 seconds, DTC U1XXX (where XXX is equal to the identification number) is set. Use DTC ID NUMBER  table to determine which module is not communicating.

When more than one loss of communication DTC is set in one or more modules, perform diagnosis in the following order:

• Current DTCs before history DTCs, unless otherwise indicated in testing procedure.
• DTC that was reported the most times.
• From lowest number DTC to highest number DTC.