Allison 1000 & 2000 Gen 5 Fault Code:U0100 Lost Communication With ECM A

CIRCUIT DESCRIPTION:
This test detects the loss of certain messages from the CAN Bus.

ACTION TAKEN WHEN THE DTC SETS:
1. The CHECK TRANS light is not illuminated.
2. DTC is stored in TCM history.
3. Default values are substituted for missing data, e.g., engine throttle percentage, engine torque, engine coolant temperature.

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The DTC automatically clears the DTC from the DTC history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
DTC U0100 indicates that a CAN bus hardware error has occurred. This code may be caused by:
1. Miswired or defective OEM controllers, OEM components, or OEM circuits attached to CAN.
2. Defective TCM.

The diagnostic tool Data Bus Viewer may be selected from the File Menu to monitor or log SAE J1939 datalink messages.

An active DTC U0100 may prevent the diagnostic tool from communicating with the TCM. The J-47276 TCM Reflash Harness may be used to confirm that the TCM is operational. Connect the TCM Reflash Harness to the TCM and leave the OEM harness disconnected. Provide input power for the J-42455-A Load Box.

CAN1 and CAN2 devices must not be interconnected because they are not compatible with each other.

For proper datalink communications, it is necessary to have two 120 Ω resistors installed in parallel across the CAN High and CAN Low terminals. Resistance across CAN High and CAN Low should measure 60 Ω when wired correctly.

NOTE: The OEM transmission warranty, or the extended coverage for parts and labor, does not cover the repair or replacement of OEM or bodybuilder provided components or any external wire harnesses not provided by the OEM.

Before repairing or replacing these components or circuits that caused a transmission issue, always contact the vehicle OEM call center and/or the vehicle OEM or bodybuilder service representative to verify the warranty coverage and proper payment arrangements, arrange an alternate sublet or repair plan (if needed), and get troubleshooting assistance for the repair (such as vehicle schematics, DTC trees, parts assistance, etc.).