GM/Detroit 6.5L ENGINE CONTROLS – DTC U1026 Loss of ATC Class 2 Communication

Circuit Description
The PCM monitors the serial data (class II) circuit for communications from the Automatic Transfer Case (ATC) controller. If the ATC controller is not communicating with the PCM this DTC will set.

Conditions for Setting the DTC
No serial data (class II) from ATC controller to the PCM.

Action Taken When the DTC Sets
This DTC wil l not illuminate the MIL.

Conditions for Clearing the MIL/DTC
• A History DTC will clear after 40 consecutive warm up cycles with no failures of any non-emissions related diagnostic test.
• PCM battery voltage is interrupted.
• Use of a scan tool.

Diagnostic Aids
This DTC will not set unless the PCM and ATC controllers have already establish communications first. This DTC will only diagnosis an open or intermittent connection from the ATC controller to the splice.

Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table.
1. In this step, the Powertrain OBD System Check is being performed.


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