Allison 3000 & 4000 Gen 4 Fault Code: U0442 Invalid Data Received From ECM/PCM B (CAN1/J1939)

DIAGNOSTIC RESPONSE:
None

CIRCUIT DESCRIPTION:
In OEM 4th Generation Controls, the preferred digital datalink is the SAE J1939 Controller Area Network (CAN). The Transmission Control Module (TCM) communicates with the engine control module and other controllers by exchanging standardized digital messages over SAE J1939. The physical network consists of a two-wire twisted pair, two 120 Ω termination resistors and, in most cases, a third shield wire. A 120 Ω termination resistor is located at each end of the network. Vehicle OEMs may choose to install external termination resistors or use internal termination resistors built into many SAE J1939 electronic modules, including the TCM and shift selector. Refer to the OEM Technician’s Library for additional information.

CONDITIONS FOR RUNNING THE DTC:
1. After TCM initializes normally and engine speed is above 200 rpm for more than 5 seconds, this DTC test will run at 0.1 second intervals.
2. SAE J1939 EC1 engine controller message is available.

CONDITIONS FOR SETTING THE DTC:
DTC U0442 sets when the TCM detects engine derate in the Engine Configuration (EC) message sent by the engine controller. The TCM defines engine derate when the EC message contains current maximum engine torque or power data that is less than the TCMs learned maximum engine torque or power.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM does not illuminate the CHECK TRANS light.
2. DTC is stored in the TCM history.
3. TCM substitutes percent load for accelerator pedal position and adjusts shift schedule.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
Use the diagnostic tool to clear the DTC 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.

DTC U0442 is self-clearing when engine derate is not active.

DIAGNOSTIC AIDS:
DTC U0442 indicates engine is derating. This DTC may be caused by:
– Engine DTCs.
– Low engine power.