Section 07: TRANSMISSION
PA1562
20
FIGURE 15: AIR PRESSURE REGULATOR (TYPICAL) 07130
9. ALLISON AUTOMATIC TRANSMISSION
TROUBLESHOOTING
For complete information about Allison
transmission troubleshooting, refer to ‘’Allison 4
th
Generation Controls – Troubleshooting Manual:
3000 and 4000 Product families (TS3989)”.
9.1 4
TH
GENERATION TRANSMISSION
CONTROL MODULE
FIGURE 16: TRANSMISSION CONTROL MODULE 07140
The Allison transmission has a new Transmission
Control Module (TCM) which involves specific
diagnostic incident codes. The TCM unit is located
in the coach rear electrical compartment.
TCM Replacement
The TCM is a non-serviceable electronic device.
When it fails, it must be replaced using the
following procedure:
o Open the coach rear baggage compartment
then remove the rear electrical compartment
door in order to get access to the TCM;
o Remove the electrical cable connectors;
o Unscrew the TCM unit;
o Replace by reversing the procedure.
CAUTION
Place the battery master switch to the ‘’OFF’’
position.
9.2 DIAGNOSTIC TROUBLESHOOTING
CODES (DTC) — ALLISON 4TH
GENERATION CONTROLS
Diagnostic codes (DTC) are numerical
indications relating to a malfunction in
transmission operation. These codes are logged
in a list in the TCM memory with the most
severe or most recent code listed first. A
maximum of five codes (numbered d1 to d5)
may be listed in memory at one time. As codes
are added, the oldest inactive 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 (DTC) and code information
may be accessed through the pushbutton shift
selector or using an Allison DOC™ diagnostic
tool.
The TCM separately stores the active and
inactive codes. An active code is any code that
is current in the TCM decision-making process.
Inactive codes are codes that are retained in the
TCM memory and will not necessary affect the
TCM decision-making process. Inactive codes
are useful in determining if a problem is:
• Isolated ;
• Intermittent ;
• Result from a previous malfunction.
The TCM may automatically
delete a code from memory if it
has not recurred. If the MODE
INDICATOR (LED) is not
illuminated, the displayed code is
not active. An illuminated MODE
INDICATOR (LED) during normal
operation signifies secondary shift
mode operation.
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