Allison 1000 & 2000 Gen 4 Fault Codes: U0031 J1850 (Class 2) Serial Data Communication Link Low

Allison 1000 & 2000 Gen 4 Fault Codes: U0031 J1850 (Class 2) Serial Data Communication Link Low

CIRCUIT DESCRIPTION:
Applications that employ J1850 class 2 serial communication use wire 130 to send operational information and commands among the various control modules. Included modules would be Powertrain Control Module (PCM), Antilock Brake System (ABS) Controller, 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.

CONDITIONS FOR RUNNING THE DTC:
The components are powered and ignition voltage is greater than 9V and less than 1 BV (12V TCM) or greater than 1 BV and less than 32V (24V TCM).

CONDITIONS FOR SETTING THE DTC:
DTC U0031 is set when low voltage is detected on the class 2 data circuit for more than 3 seconds. This would normally indicate a short-to-ground at wire 130.

ACTION TAKEN WHEN THE DTC SETS:
1. The CHECK TRANS light does not illuminate.
2. DTC U0031 is stored in the TCM history.
3. TCM uses default values for missing/erroneous information.
4. 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 this DTC when software detects a failure recovery has occurred.

DIAGNOSTIC AIDS:
1. If communication can be established with the Scan Tool at the OBDII connector, then the U0031 should be shown in failure records only. This may indicate that an intermittent short-to-ground was present at one time. Refer to Identification of Potential Circuit Problems information.
2. It is not possible to communicate with J1850 with this DTC active.
3. Use the J 43890 T-harness to communicate with the TCM to determine if the U0031 is still active.
4. U0031 in failure records may be present along with a U1000-U1096 that is active. This would indicate that the malfunction occurred when the ignition was ON.
5. This code indicates that voltage is low at wire 130. Normally, this is an indication that a short-to-ground exists at wire 130. Inspect wire 130 for this condition.

Inspect wire 130 for poor electrical connections at the TCM. Look for the following conditions:
1. A bent terminal.
2. A backed-out terminal.
3. A damaged terminal.
4. Poor terminal tension.
5. A chafed wire.
6. A broken wire inside the insulation.

When this DTC is active an engine no-start condition may exist. Class 2 messages will not be sent to enable the fuel pump and starter.