INTRODUCTION
Continued illumination of the
CHECK TRANS
light during vehicle operation
(not start-up) indicates the TCM/ECU has signaled a diagnostic code. Poor
performance may activate a code without illuminating the
CHECK TRANS
light.
Up to
fi
ve diagnostic codes can be recorded. Diagnostic codes can be read and
cleared by two methods: by using the shift selectors shown below or using the
Allison DOC™ Diagnostic Tool for the PC or PDA. Use of the Allison DOC™
Diagnostic Tool for the PC or PDA is described in the instruction manual
furnished with each tool. Basic information on code reading, code clearing and
troubleshooting is covered in this DIAGNOSTICS section. For additional
information, refer to TS3989EN Troubleshooting Manual for Allison 4
th
Generation Controls. More detailed information is available in the Troubleshooting
Manual. Refer to the SERVICE LITERATURE section for the appropriate
publication number.
DIAGNOSTIC CODES
Diagnostic codes are numerical indications relating to a malfunction in
transmission operation. In WTEC III Controls, each code consists of a two-digit
main code and a two-digit subcode. In Allison 4
th
Generation Controls, each code
consists of
fi
ve characters. The
fi
rst character is a letter followed by a four digit
numeric string. These codes are logged in a list in the TCM/ECU memory with
the most severe or otherwise most recent code listed
fi
rst. A maximum of
fi
ve
codes (numbered d1–d5) may be listed in memory at one time. As codes are
added, the oldest non-active code is dropped from the list. If all codes are active,
the code with the lowest priority that is not included on the severity list is
dropped from the list. Access to the diagnostic codes and code information is
through the pushbutton and lever shift selectors or the diagnostic data reader.
The TCM/ECU separately stores the active and historical (non-active) codes. An
active code is any code that is current in the TCM/ECU decision-making process.
DIAGNOSTICS
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