Allison 1000 & 2000 Gen 4 Fault Codes: U1000 Class 2 Loss of Serial Data Communication

Allison 1000 & 2000 Gen 4 Fault Codes: U1000 Class 2 Loss of Serial Data Communication

CIRCUIT DESCRIPTION:
Applications that employ J1850 class 2 serial communication use wire 130 to send operational information and commands among the various control modules. The control modules included are the Powertrain Control Module (PCM), Antilock Brake System Controller (ABS), Truck Body Controller (TBC) and Instrument Panel Cluster (IPC). Each controller sends out a state of health (SOH) message approximately once every second. The TCM uses these SOH messages to monitor the condition of the devices on the class 2 serial link.

The following DTCs identify the specific controller noted:
DTC Number – Control Module:
1. U1000 – Class I I-Loss of Serial Data Communication
2. U1016 – Powertrain Control Module (PCM)
3. U1041 – Antilock Brake System Module (ABS)
4. U1064 – Truck Body Controller Module (TBC)
5. U1096 – Instrument Panel Cluster Module (IPC)

CONDITIONS FOR RUNNING THE DTC:
The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 18V and less than 32V (24V TCM).

CONDITIONS FOR SETTING THE DTC:
DTC U1000 – U1096 is set when the TCM has not received a state of health (SOH) message from the Control Module indicated for a period of time exceeding 2 seconds.

ACTION TAKEN WHEN THE DTC SETS:
1. The CHECK TRANS light does not illuminate.
2. DTC U1000-U1096 is stored in the TCM history.
3. TCM uses default values for missing/erroneous information.
4. For U1016 only-the TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to clear the code from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring. The TCM self-clears the DTC when the software detects a failure recovery has occurred.

DIAGNOSTIC AIDS:
1. An intermittent open between a module and the connector node may cause this DTC to set.
2. A poor connection at a module or the connector node may cause this DTC to set.
3. An intermittent open in a connector node may cause this DTC to set.
4. An open voltage or ground circuit to a module may cause this DTC to set.
5. An internal module malfunction may cause this DTC to set.