Section III. TROUBLESHOOTING
This section provides troubleshooting information to diagnose and correct engine malfunctions in conjunction with
troubleshooting procedures in TM 9-2320-273-20 and TM 9-2320-273-34 for M915/Big Cam I and TM 9-2320-283-20 and
TM 9-2320-283-34 for M915A1/Big Cam III. For further engine troubleshooting information, refer to the Cummins troubleshooting and
repair manual, NT 855 Engines, Bulletin No. 3810298-00.
The troubleshooting procedures are organized by malfunction, followed by steps instructing you to perform a test or inspection
to determine the corrective action required. The corrective action is then provided and the appropriate procedure paragraph number(s)
is given. The steps listed under each malfunction are in the order in which the causes are most likely to occur.
Operation of a deadlined vehicle without preliminary inspection will cause further damage to
a malfunctioning component and possible injury to personnel.
Check all tags, service request forms, and vehicle logbooks for repair history. This may lead to the source of the problems.
Debrief the operator (if possible) for a general description of the problem, then attempt to verify the fault. If the same fault is
observed, refer to the troubleshooting symptom index for the precise troubleshooting malfunction and procedures.
Before correcting a problem, diagnose the cause of the problem. Do not allow the same failure to occur again. Engines very
often are disassembled in search of the problem and the real evidence to its cause is destroyed. Check again to ensure an easier
solution has not been overlooked.
When troubleshooting, always check the easiest and most obvious things first. This simple rule saves time and trouble. For
example, low power complaints are often the result of loose throttle linkage, dirty fuel, or clogged air filters, and excessive oil
consumption is often the result of leaky gaskets or loose line connections.
Doublecheck before disassembly. The source of many engine problems can be traced to more than one part in a system. For
example, excessive fuel consumption may not be caused by the fuel pump alone. Instead, the trouble could be a clogged air cleaner or
a restricted exhaust passage causing severe back pressure.
If a fault is not discovered until out-of-truck maintenance of the engine, refer to the troubleshooting procedures as necessary at
a point where the fault is encountered for further diagnosis.