Allison Transmission 3000 Mechanic's Tips page 42

Whenever the CHECK TRANS light is illuminated, the ECU logs a diagnostic
code in memory. The diagnostic codes can be accessed through the shift selector
display or through the Allison DOC™ service tool.
NOTE: Diagnostic codes can be logged without illuminating the
CHECK TRANS light. This occurs when the ECU senses a problem
but determines that the problem will not cause immediate transmission
damage or dangerous performance.
b. Diagnostic Codes. Diagnostic codes are stored in memory. Up to five codes,
in memory positions d1 through d5, can be stored, with the most recently stored
code displayed first.
Code List
Position Code*
*
d1
d2
d3
d4
d5
* Displayed on shift selector and Allison DOC™ service tool
** YES = mode indicator (LED) illuminated
† Accessible by Allison DOC™ service tool
Diagnostic codes consist of a two-digit main code and a two-digit subcode (refer
to Table 2–10).
• Main codes are listed first and provide the general condition or area of a
fault detected by the ECU.
• Subcodes are listed second and provide specific areas or conditions within
the main code that caused the fault.
• Example of Code 13 12:
— 13 indicates a problem with ECU voltage
— 12 indicates the problem is caused by low voltage
• Example of Code 32 12:
— 32 indicates a problem with the throttle position sensor signal
— 12 indicates that the throttle position sensor signal is low
Diagnostic codes are displayed one character or digit at a time. Table 2–11 is an
example of code 21 12. Each character or digit is displayed for about one second.
Table 2–10. Diagnostic Codes Overview
Main
Subcode*
21 12
41 12
23 12
34 12
56 11
Active
Indicator Counter
**
YES
YES
NO
NO
NO
41
Ignition
Cycle Event
Number†
†
00
00
08
13
22
10
04
00
02
02