TM 5-2350-378-23&P
FIELD MAINTENANCE
INTRODUCTION TO USING THE HYDRAULIC DIAGNOSTIC CENTER (HDC) SYSTEM TO TROUBLESHOOT
THE M9 ACE HYDRAULIC SYSTEM
INTRODUCTION
This work package contains information needed when troubleshooting the M9 ACE hydraulic system using the
Hydraulic Diagnostic Center (HDC) System. It includes information for preparing the HDC System for use and
procedures for performing a Functional Check-Out of the HDC System, both as a weekly PMCS check of the HDC
System integrity, and as the initial step in using the HDC System to aid in troubleshooting the M9 ACE hydraulic
system.
This work package describes the differences between troubleshooting the M9 ACE hydraulic system with, and
without, the HDC System, and explains the additional items that need to be considered when using the HDC System
to aid in troubleshooting the vehicle hydraulic system. Information as to how to use the HDC System to aid in
troubleshooting the M9 ACE hydraulic system is included as well as information to aid in troubleshooting the specific
HDC System hydraulic and electrical circuits, when used with the HDC System troubleshooting work package
The HDC System is an aid, used to assist in the troubleshooting of the M9 ACE hydraulic system. The HDC is not
an independent diagnostic tool; it does not provide an automated or semi-automated means of localizing hydraulic
faults. The use of the HDC System allows the amount of time required to isolate faults and malfunctions in the vehicle
hydraulic system to be dramatically reduced, when compared to the time required to troubleshoot the vehicle
hydraulic system without the HDC System.
TROUBLESHOOTING THE HDC SYSTEM
Using the HDC System does introduce some additional factors that should be considered when troubleshooting the
vehicle hydraulic system. Components of the HDC System are located throughout the M9 ACE vehicle and, although
they simplify the actual troubleshooting process, they also introduce additional components that interface with the
previously existing vehicle hydraulic system, that also can fail or malfunction like any other component.
To aid in the troubleshooting of the M9 ACE hydraulic system, the HDC System must be operating properly, and
there must be some way to assess the operational status of the HDC System. The M9 ACE HDC System Functional
Check-Out (WP 0025) provides the means for the maintainer to easily check portions of the HDC System to
determine if the HDC System is functionally operational.
When the HDC System is to be used (for troubleshooting the vehicle hydraulic system or when just being functionally
checked as part of a PMCS requirement), the M9 ACE HDC System Functional Check-Out (WP 0025) should first
be performed. If the HDC System does not pass all portions of the Functional Check-Out, refer to (WP 0021) and
proceed to troubleshoot the HDC System as indicated.
Aside from the HDC Control Box and three electrical cables integrated into the vehicle, two main types of components
comprise the HDC System; solenoid valves and hydraulic pressure transducers. Although both of these types of
components are very reliable (as are the electrical cables), they can possibly fail like other electrical and hydraulic
components. The solenoid valves are spring-loaded and can possibly fail in two ways. They can fail to energize, and
they can fail to return to the original de-energized state (valve spool does not return to the de-energized state), when
energizing (supply) voltage is removed. The probability of a solenoid valve being stuck (the valve spool does not
return to the de-energized position) is very low and would only occur after a hydraulic maintenance test was
performed in which the valve had been energized. The actual movement (or non-movement) of the valve spool
cannot be detected by the HDC Control Box as part of the System BIT. The solenoid valves are normally not
energized. They are only energized upon command, and are supplied 24 VDC only when energized. Normally all
solenoid valves are de-energized (reset) and are not supplied any voltage.
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