ALLISON 1000 AND 2000 PRODUCT FAMILIES ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL
DIAGNOSTIC TROUBLE CODES (DTC)
DTC U0073 (Previously U2104) CAN Bus Reset Counter Overrun
determined
by Engine
OEM
"""'- Attached to
ECM via
Deutsch/P
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TERMINATION
triangle 3-pin exceed 1 meter RESISTOR
c connector c c
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I en I en I en
SHIELD
131 GREEN �
+ -- --� + 129 -- --� +
+
120Q I I 120Q
SHIELD I 132 SHIELD I BLACK I SHIELD I
RESISTOR RESISTOR
L.----- L.----- L.-----
,_ CONTROLLER AREA NETWORK (CAN) _,
Should not exceed 40 meters
SAE J1939-11 V06460.01.00
Circuit Description
J1939 is the protocol currently used in medium duty applications to allow communication between an
electronically-controlled engine and the Allison 1000 and 2000 Product Families transmission. A signal is sent over
a two-wire network harness that incorporates two 120 Ohm resistors in parallel. There are two versions of J1939
currently in use in the medium duty market. Version J1939-11, the most widely used, incorporates a third shield
wire. There is also J1939-15, which uses a two-wire connection without shielding.
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).
• Engine speed is greater than 200 rpm and less than 7500 rpm for 5 seconds.
Conditions for Setting the DTC
OTC U0073 is set when the TCM detects no communication on the Controller Area Network (CAN) backbone
harness for 3 seconds or more. This may be due to a shorted wire to ground or power in the CAN backbone
harness.
Action Taken When the DTC Sets
• OTC U0073 is stored in the TCM history.
• The CHECK TRANS light does not illuminate.
• The TCM defaults to the last-used adaptive shift values and engine throttle percentage is calculated from
torque clip speed.
• The TCM freezes shift adapts (DNA).
5-250 Copyright© 2004 General Motors Corp.
ALLISON 1000 AND 2000 PRODUCT FAMILIES ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL
DIAGNOSTIC TROUBLE CODES (DTC)
Conditions for Clearing the DTC/CHECKTRANS 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 OTC recurring.
Diagnostic Aids
• If communication can be established at the vehicle nine-pin connector and U0073 is listed in failure records,
this indicates an intermittent short condition was present.
• When diagnosing for intermittent shorts-to-ground, massage the wiring harness while watching the test
equipment for a change. Refer to Section 4, Wire Check Procedures.
• If an active U0073 is present, Scan Tool communication will not be possible. The cause of the active DTC must
be discovered and repaired before communication can be established with the TCM.
• A short between wires 129 and 132 within the CAN harness can cause this DTC.
• A short between wires 129 and 131 within the CAN harness can cause this DTC.
• A short to a vehicle ground and wire 129 can cause this DTC.
• A short to vehicle power and wire 132 can cause this DTC.
• Inspect the wiring for poor electrical connections at the TCM. Look for the following conditions:
A bent terminal.
A backed-out terminal.
A damaged terminal.
Poor terminal tension.
A chafed wire.
A broken wire inside the insulation.
• For proper data communications it is necessary to have two 120 Ohm resistors installed in parallel at the J1939
CAN backbone harness.
• If this DTC is present in a new vehicle, harsh shifting may occur due to adaptive function inhibit (DNA).
Test Description
The number below refers to the step number on the diagnostic table.
3. This step inspects the CAN backbone harness for shorts-to-ground or power.
5. This step checks TCM function.
DTC U0073 CAN Bus Reset Counter Overrun
Step Action Yes No
1 Was the Beginning The Troubleshooting Process Go to Step 2 Go to
(Paragraph 5-4A) performed? Beginning The
Troubleshooting
Process
(Paragraph 5-4A)
2 1. Install the Scan Tool. Go to Diagnostic Go to Step 3
2. Turn the ignition ON with the engine OFF. Aids
Is Scan Tool communication possible at the diagnostic
connector?
Copyright© 2004 General Motors Corp. 5-251
ALLISON 1000 AND 2000 PRODUCT FAMILIES ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL
DIAGNOSTIC TROUBLE CODES (DTC)
DTC U0073 CAN Bus Reset Counter Overrun (cont'd)
Step Action Yes No
3 1. Inspect wires 129 (positive), 132 (negative), 131 (shield) Go to Step 4 Go to Step 5
at engine and transmission connectors for a possible
shorting condition or terminal damage.
NOTE: No Scan Tool communication is possible when
this DTC is active.
2. This OTC indicates that a CAN bus hardware error has
occurred. This may indicate a short-to-power or ground
has occurred at the CAN bus wiring harness.
Was a wiring problem found?
4 NOTE: The vehicle OEM has responsibility for all Go to Step 7 Go to Step 4
external wiring harness repair. Harness repairs
performed by Allison Transmission distributors and
dealers are not covered by Allison Transmission
warranty.
Repair the vehicle J1939 CAN wiring harness.
Is the repair complete?
5 Switch the current TCM with a known good unit. Check for Go to Step 6 -
proper communication. If this repairs the condition, reinstall
the "defective" TCM to verify the TCM failure and then
install a new TCM.
Is replacement complete?
6 In order to verify your repair: Begin the System OK
1. If communication is established with the Scan Tool, clear diagnosis again.
the OTC. Go to Step 1
2. Use the Scan Tool, in the test passed section, to confirm
the diagnostic test was run.
Did the OTC return?
5-252 Copyright© 2004 General Motors Corp.
