DIAGNOSTIC TROUBLESHOOTING CODES (DTC) — ALLISON 5TH GENERATION
CONTROLS
Diagnostic features are provided with the transmission control system to assist in troubleshooting of
malfunctions and/or the monitoring of specific operating parameters.
NOTE: You will find the complete transmission operation instructions and driving tips in the Allison
5th & 6th Generation Operator’s Manual 3000_ 4000 Series available on the Prevost Technical
Publications site
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 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.
Shows active DTC P0730
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-1652 Operator's Manual H3-45 Coach
Allison Transmission Other Features C-7
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