PREVOST X3-45 COMMUTER 2018 Operator'S Manual Download

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APPENDIX B – Allison Transmission’s Other Features 12-3

PA1633 X3-45 Commuter Operator’s Manual

DIAGNOSTIC TROUBLESHOOTING CODES (DTC) — ALLISON 5TH GENERATION

DIAGNOSTIC TROUBLESHOOTING CODES (DTC) OVERVIEW

Diagnostic features are provided with the transmission control system to assist in troubleshooting of
malfunctions and/or the monitoring of specific operating parameters. 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 character 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 DIAGNOSICS 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 diagnostics mode times out and returns the selector to normal operating mode
after approximately 10 minutes of operator inactivity.

Diagnostic Code Display and Clearing Procedure

Diagnostic codes can be read and cleared by two methods:

Using an Allison DOC™ diagnostic tool. For specific instructions on how to use an Allison DOC™

diagnostic tool, refer to the User Guide.

Using the pushbutton shift selector.

To begin the diagnostic process:

1. Bring the vehicle to a stop at a safe location.

2. Apply the parking brake.