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U1026 means is a PCM communication fault, the computer has detected a fault.
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the 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 monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is XXXXX by a module, it will monitor for that modules Node Alive message. Each module ON the class 2 serial data circuit 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 from a learned identification number for 5 seconds, a DTC U1xxx is set.
The Control Module ID Number list provides a method for determining which module is not communicating. A module with an internal class 2 serial data circuit malfunction or which loses power during the current ignition cycle would have a Lost Communication DTC set by other modules. Use the Control Module ID Number list in order to determine which module is not communicating and the Lost Communications with XXX diagnostic table in order to diagnose the malfunction. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx is set.
Powertrain Control Module (PCM)
Transmission Control Module (TCM)
Tranfer Case Shift Control Module w/4WD
Electronic Brake Control Module (EBCM)
Rear Wheel Steering Control Module
Body Control Module (BCM)
Inflatable Restraint Sensing and Diagnostic Module (SDM)
Instrument Panel Cluster (IPC)
Driver Information Center (DIC)
Vehicle Interface Unit (VIU)
HVAC Control Module
Memory Seat Module (MSM)