When the CHECK TRANS light comes on and the ignition switch is turned off,
the transmission will remain in N (Neutral) until the condition causing the
CHECK TRANS light is corrected.
Generally, while the CHECK TRANS light is on, upshifts and downshifts will be
restricted and direction changes will not occur. Lever and pushbutton shift
selectors do not respond to any operator shift requests while the CHECK
TRANS light is illuminated. The lockup clutch is disengaged when transmission
shifting is restricted or during any critical transmission malfunction.
DIAGNOSTIC CODES
Diagnostic Codes Overview. Diagnostic codes are numerical indications relating
to a malfunction in transmission operation. These codes are logged in a list in the
TCM/ECU memory with the most severe or most recent code listed first. A
maximum of five 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.
Diagnostic codes and code information may be accessed through the pushbutton
and lever shift selectors or using an Allison DOC™ diagnostic tool.
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.
Historical codes are codes that are retained in the TCM/ECU’s memory and will
not necessarily affect the TCM/ECU decision-making process. Historical codes are
useful in determining if a problem:
• Is isolated.
• Is intermittent.
• Results from a previous malfunction.
The TCM/ECU may automatically delete a code from memory if it has not
recurred.
If the MODE INDICATOR (LED) is illuminated, the displayed code is active. If
the mode indicator (refer to Figure 7 and Figure 8) is not illuminated, the
displayed code is not active. An illuminated mode indicator during normal
operation signifies secondary mode operation.
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