Allison 3000 & 4000 Gen 4 Fault Code: U0001 Hi Speed CAN2 Bus Reset Counter Overrun (CAN2/IESCAN)

DIAGNOSTIC RESPONSE:
Use default values, inhibit SEM

CIRCUIT DESCRIPTION:
Beginning MY07, OEM 4th Generation Controls Transmission Control Modules (TCMs) were capable of communicating with some Mercedes engines via the IESCAN on CAN2. Beginning with January 2011 software, TCMs were capable of communicating on high -speed SAE J1939 (500 kbps) on CAN2. The TCM uses the high-speed Controller Area Network 2 (CAN2) chip to exchange standardized messages with the engine controller and other vehicle systems. The IESCAN and SAE J1939 CAN2 physical network consists of two-wire twisted pair, two 120 Ohm resistors and, in most cases, a third shield wire and CAN2 capable controllers. A 120 Ohm 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 electronic modules. CAN2 capable modules include the TCM and shift selector. Refer to the OEM Technician’s Library for additional information.

NOTE: Some applications may use the Type 2 (Green), SAE J1939-13, 9-Pin service tool connector for CAN-2 installations instead of the SAE J2284 trapezoidal connector. Refer to the OEM Technician’s Library for wiring information.

CONDITIONS FOR RUNNING THE DTC:
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.

CONDITIONS FOR SETTING THE DTC:
DTC U0001 sets when the TCM detects no communication on the CAN2 datalink for 0.2 seconds or more.

ACTION TAKEN WHEN THE DTC SETS:
1. The TCM does not illuminate the CHECK TRANS light.
2. DTC is stored in TCM history.
3. SEM operation is not active, if applicable.
4. Default values are substituted for missing data, e.g., engine throttle percentage, engine torque, engine coolant temperature.
5. SAE J1939 Shift Selector input (if on CAN2 ) is lost (fails over to W134 directional signal).
6. The TCM freezes shift adapts (DNA).

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.

DIAGNOSTIC AIDS:
1. DTC U0001 indicates that a CAN2 bus hardware error has occurred.
This code may be caused by:
– Miswired or defective OEM controllers, OEM components, or OEM circuits attached to CAN2.
– Defective TCM.
– Defective shift selector.
2. Vehicle manufacturers may use the following terminal pairs for CAN2 high and low wires:
– Terminals 6 and 27.
– Terminals 66 and 47.
– Both terminals 6 and 27 and terminals 66 and 47 are wired in a pass-through setup.
3. Vehicle manufacturers may wire the TCM into the CAN2 backbone in three different ways:
– The TCM may be on its own stub as in traditional CAN backbones.
– The TCM may be wired in a pass-through configuration such that the CAN high and low wires are
connected to two separate pin pairs in the TCM 80-way connector. Datalink messages pass-through
but can still be viewed by the TCM.
– The TCM may represent one end of the backbone. Typically, the internal resistor in the TCM will be
used in this setup.
4. An active DTC U0001 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 from the J-42455-A Load Box.
5. CAN1 and CAN2 devices must not be interconnected because they are not compatible with each other. CAN1 operates at 250 kbps data rate and CAN2 operates at 500 kbps data rate.
6. The diagnostic tool will not communicate on CAN2 without appropriate translator, cables, and translator drivers. Refer to the diagnostic tool Help menu and User Guide for more information about service tool connection requirements for CAN2.
7. For proper datalink communications, it is necessary to have two 120 Ω resistors installed in parallel across the CAN2 High and CAN2 Low terminals. Resistance across CAN2 High and CAN2 Low should measure 60 Ω when wired correctly.

Review applicable information in the OEM Technician’s Library, General Troubleshooting of Performance Complaints – Shift Selector Issues, Control System and Transmission Specifications, and other related information.