DTC U1001 & U1254: Loss Of XXX Communications: Description

Serial data line is used to communicate information and commands between modules. When a module receives a message for a critical operating parameter (Node Alive message), module records ID number of module which sent message for State Of Health (SOH) monitoring. Once an ID number is learned by a module, it will monitor for that module's Node Alive message. Each module on serial data line is required to send a Node Alive message every 2 seconds. When no message is detected from a learned ID number for 5 seconds, DTC U1XXX (XXX is equal to 3-digit identification number) will set. Use DTC SUFFIX IDENTIFICATION  table to determine which system is not communicating. For example, if DTC U1016 is set, Powertrain Control Module (PCM) is not communicating. A module with a class 2 serial data line malfunction or which loses power during a current ignition cycle will have a loss of communication DTC set by other modules that depend on information from that failed module. Modules that can communicate will set a DTC indicating module can not communicate. DTC U1000 or U1255 will set, when voltage supplied to module is in normal operating voltage range of 9-16 volts. DTCs U1300, U1301 or U1305 do not have a current status. Vehicle power mode requires serial data communication to occur.

If more than one loss of communication DTC is set in either one or multiple modules, perform diagnosis in following order:

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