Allison Transmission Troubleshooting; Diagnostic Troubleshooting Codes (Dtc) - Allison 5Th Generation Controls - PREVOST H3-41 Maintenance Manual

23. Install engine splash guards.
24. Adjust the retarder pressure to 80 ± 3 psi with
the air pressure
information refer to Section 12, "BRAKE AND
AIR SYSTEM",
PRESSURE REGULATOR". The air pressure
regulator is located at back of engine
compartment, on R.H. side (Figure 14) or in
the R.H. side rear service compartment.
25. Make sure that the drain plug is in place, and
then remove the transmission dipstick and
pour approximately 24 US quarts (23 L) of
automatic transmission fluid through the filler
tube. Check and adjust oil level.
CAUTION
Do not overfill the transmission. Overfilling can
cause oil aeration (milky appearance) and
overheating. If overfilling occurs, drain oil as
required to bring it to the proper level.
FIGURE 14: AIR PRESSURE REGULATOR (TYPICAL)
6. ALLISON TRANSMISSION
TROUBLESHOOTING
The Allison transmission has a new Transmission
Control Module (TCM) which involves specific
diagnostic incident codes. The TCM unit is located
in the coach main power compartment.
regulator. For more
under heading "AIR
SECTION 07: TRANSMISSION
FIGURE 15: TRANSMISSION CONTROL MODULE
TCM Replacement
The TCM is a non-serviceable electronic device.
When it fails, it must be replaced using the
following procedure:
 Open the coach main power compartment in
order to get access to the TCM;
 Remove the electrical cable connectors;
 Unscrew the TCM unit;
 Replace by reversing the procedure.
CAUTION
Place the battery master switch to the ''OFF''
position.
6.1 DIAGNOSTIC TROUBLESHOOTING
CODES (DTC) — ALLISON 5TH
GENERATION CONTROLS
Diagnostic features are provided with the
transmission control
troubleshooting of
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
PA1621 Maintenance Manual All Series | January 2017
(07140)
system to assist
malfunctions and/or the
21
in