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troubleshooting of malfunctions and/or the
monitoring of specific operating parameters.
DIAGNOSTIC TROUBLESHOOTING CODES
(DTC) OVERVIEW
When a control system malfunction is detected, a
series of Diagnostic Trouble Codes (DTCs) are
used to identify and clarify the nature of the
malfunction. These DTCs are each named by a 5
characters alphanumeric string that refers to a
diagnostic algorithm running pass/fail tests to
help identify a malfunction in the transmission or
vehicle operation. Most DTCs have some kind of
diagnostic response that the operator notices,
such as an illuminated CHECK light, selector
display change, lock in range, or inhibit shifts
condition.
DTCs are logged in the Transmission Control
Module (TCM) memory by severity and by their
active/inactive status with the most severe and
active codes listed first. A maximum of five DTCs
(numbered d1- d5) from most recent to oldest
may be read from the shift selector. As DTCs are
added, the oldest inactive DTC (historic) is
dropped from the list. If all DTCs are active, the
DTC with the lowest priority is dropped from the
list.
An active code is any code that is current in the
TCM decision-making process and has failed the
DTC test (s) associated with that specific
diagnostic algorithm. Historical codes, which are
by definition inactive, are codes that are no longer
failing their algorithm but are retained in the TCM
in order to help the technician analyze possible
causes and provide them direction if the vehicle is
brought in before they are cleared from the
queue.
DTCs can be cleared manually by the operator or
they clear automatically from last (d5) to first (d1)
in the queue after a number of engine starts,
without becoming active again.
USING SHIFT SELECTOR FOR ACCESSING
DIAGNOSTIC INFORMATION
DTCs can be displayed on the display portion of
the shift selector. A DTC is either active or
historic. An active DTC is a DTC that is current in
the TCM decision-making process. Historic DTCs
are retained in the TCM memory and do not
DOB 1300-1556
Allison Transmission Other Features B-3
necessarily affect the TCM decision- making
process.
Display Sequence
Up to five DTCs may be displayed one at a time
from the selector once the diagnostic display
mode has been initiated by the operator. Each
DTC is 5 characters in length. The DTC status
active or inactive is shown below the DTC.
The operator presses the MODE button to read
the next OTC in the queue (if any) or requests to
exit diagnostics mode. The diagnostic mode
times out and returns the selector to normal
operating mode after approximately 10 minutes
of operator inactivity.
PA-1639 Operator's Manual 2020 X3-45 Commuter
Shows active DTC P0730
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Table of Contents
Troubleshooting
