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John, GMC Technician
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Experience:  ASE MASTER TECHNICIAN/40 years experience
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What does the Computer Code U1026 mean?

Resolved Question:

What does the Computer Code U1026 mean?
Submitted: 6 years ago.
Category: GM
Expert:  John replied 6 years ago.

Hello & Welcome to JA,

 

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.

Control Module

ID Number

Powertrain Control Module (PCM)

016

Transmission Control Module (TCM)

024

Tranfer Case Shift Control Module w/4WD

026

Electronic Brake Control Module (EBCM)

041

Rear Wheel Steering Control Module

048

Body Control Module (BCM)

064

Inflatable Restraint Sensing and Diagnostic Module (SDM)

088

Instrument Panel Cluster (IPC)

096

Driver Information Center (DIC)

097

Vehicle Interface Unit (VIU)

151

HVAC Control Module

152

Memory Seat Module (MSM)

166

Customer: replied 6 years ago.
So based upon the U1026 code, my transfer Case Control Module is bad. I ask this due to the fact that my truck will not go into 4WD?
Expert:  John replied 6 years ago.
it is a good possibility , but test those circuits first.
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