Diagnostic Troubleshooting Codes (Dtc) - Allison 5Th Generation Controls; Diagnostic Troubleshooting Codes (Dtc) Overview; Using Shift Selector For Accessing Diagnostic Information - PREVOST H3-45 VIP Owner's Manual

Allison Transmission Other Features C-7
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.

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-1638 Owner's Manual X3-45 VIP