ARMY TM 9-6115-670-14&P
4-10
Section VI. UNIT TROUBLESHOOTING PROCEDURES
4.10. GENERAL.
This section contains troubleshooting procedures to determine the probable cause of observed equipment
malfunctions. Branching logic trees are provided to isolate the faulty component and offer corrective actions
to eliminate the malfunction.
4.11. UNIT TROUBLESHOOTING PROCEDURES.
The following pages list common malfunctions that may occur during operation or maintenance of the APU,
followed by a troubleshooting procedure. Refer to the symptom index to locate the troubleshooting procedure
for the malfunction you observe. Each troubleshooting procedure consists of a branching logic tree. Perform
the test or inspection, and the recommended corrective action in the order listed in the logic tree. If the
malfunction is corrected by a specific corrective action, do not continue with any remaining steps. If the
corrective actions do not correct the malfunction, notify your supervisor or Direct Support Maintenance.
SYMPTOM INDEX
Symptom
Page
1. Engine fails to turn over. ........................................................................................................................4-11
2. Engine cranks but fails to start...............................................................................................................4-12
3. Engine starts, but stops when start-preheat switch is released ............................................................4-14
4. Engine stops suddenly...........................................................................................................................4-15
5. Engine runs erratically or misfires .........................................................................................................4-16
6. Engine does not develop full power.......................................................................................................4-19
7. Engine knocks........................................................................................................................................4-20
8. Black smoke in exhaust .........................................................................................................................4-21
9. Blue or white smoke in exhaust.............................................................................................................4-22
10. Low oil pressure.....................................................................................................................................4-23
11. Engine overheating................................................................................................................................4-24
12. Engine coolant temperature too low ......................................................................................................4-25
13. DC ammeter shows no charge when vehicle battery is low or discharged...........................................4-26
14. DC ammeter shows excessive charging after prolonged APU operation .............................................4-27
15. Excessive oil consumption.....................................................................................................................4-28
16. High oil pressure....................................................................................................................................4-28
17. Fuel mixed into lubricant oil ...................................................................................................................4-29
18. Coolant mixed into lubricant oil..............................................................................................................4-29
19. AC voltmeter does not indicate voltage .................................................................................................4-29
20. AC voltmeter indicates voltage but frequency meter is off scale...........................................................4-29
21. AC voltage fluctuates.............................................................................................................................4-29
22. Frequency fluctuates .............................................................................................................................4-29
23. Main AC contactor will not close............................................................................................................4-29
24. Oil pressure fault indicator lights ...........................................................................................................4-29
25. Water temp fault indicator lights ............................................................................................................4-29
26. Overspeed fault indicator lights .............................................................................................................4-30
27. Over-voltage fault indicator lights ..........................................................................................................4-30
