LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 1999 >> Escalade >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Communication Devices >> Data Link Communications System >> Diagnostic Tests >> DTC U1026: Loss Of Transfer Case Shift Control Module Class 2 Communication >> Diagnostic Procedures
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedures

NOTE: Do not clear DTCs without first recording freeze frame and failure records data. This information will be erased when the DTCs are cleared.
  1. Perform powertrain OBD system test. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION - GASOLINE - EXCEPT METRO, PRIZM & TRACKER article in ENGINE PERFORMANCE.
  2. Connect a scan tool and turn the ignition to ON. Do not start the engine. Establish communication with the transfer case shift control module. If the transfer case shift control module communicates with the scan tool, go to next step. If the transfer case shift control module cannot communicate with the scan tool, perform DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  3. Check the class 2 data circuit for an open between the PCM/VCM and the transfer case shift control module, a short to ground, a short to voltage or loose or damaged terminals on the DLC, PCM/VCM or the transfer case shift control module. If there is no fault with the wiring or connectors, go to next step. If there is any fault with the wiring or connectors, repair and go to step  5.
  4. Turn ignition to OFF. Connect any components or connectors that were disconnected. Save freeze frame and failure records data and clear all DTCs with the scan tool. Turn ignition OFF for 15 seconds. Operate the vehicle under the conditions indicated in the failure records. If DTC U1026 does not reset, fault is intermittent. Perform DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  5. Turn ignition OFF. Connect any components or connectors that were disconnected. Clear all DTCs with the scan tool. If any DTCs are displayed, perform DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.

The DTC will clear after 40 consecutive ignition cycles if there are no failures of any non-emissions related diagnostic tests, if power to the PCM/VCM is interrupted. DTCs can be manually cleared with a scan tool.

scientia non olet · About LEMON Manuals