Caution – C.E. Niehoff & Co. N1387-1/EPM Troubleshooting Guides User Manual
Page 7
Page 7
TG0019A
Section 5: Advanced Troubleshooting
(CONT’D)
Shut off engine. With key off, engine off: Test for battery voltage at alternator 28 V B+
terminal. Does battery voltage exist?
Yes
No
Check and repair EPM wiring and battery cables as necessary.
Continue test.
Chart 1 – 28 V LED Steady AMBER – No 28V Alternator Output – Test Charging Circuit
With DMM, check resistance across field coil. Connect red lead of DMM to socket A in alternator-to-regulator
harness plug. Connect black lead to B+ terminal on alternator. Does meter show 2.0 ± 0.2 ohms?
Yes
No
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Yes
Test phase signal into regulator (AC). Set meter to diode tester:
Connect red lead of DMM to socket C of regulator harness and black
lead to socket B. Meter should show voltage drop value.
Then reverse meter lead connections. Meter should show OL (blocking).
No
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Yes
No
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Regulator responded to overvoltage condition. Go to Chart 4
on page 9 to troubleshoot OVCO.
Figure 5 – Alternator-to-Regulator
4-Socket Harness Plug
SOCKET CONNECTIONS
A
F–
B
Phase Signal AC
C
B–
D
28 V B+
With key on, engine running: Test for battery voltage between IGN terminal on regulator and alternator
B– terminal. Does 28 V battery voltage exist?
Yes
No
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With key off, engine off: Remove alternator-to-regulator 4-pin harness from regulator. Test for battery
voltage across sockets D and C in harness plug. Does 28 V battery voltage exist?
Alternator is defective.
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Alternator is defective.
T
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Alternator is defective.
T
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Regulator is defective.
Yes
Connect jumper wire from socket A in regulator harness plug to B– terminal on alternator.
Spark will occur. Touch steel tool to shaft to detect significant magnetism. Is shaft magnetized?
No
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Repair vehicle ignition circuit wiring as necessary.
Yes
No
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CAUTION
Troubleshooting sequences must be performed during 3-minute delay after battery-connect button on
vehicle is pressed. If main LED on EPM is not flashing GREEN, press button to reactivate system. LED on
EPM must be flashing GREEN while performing tests.
Start engine. Wait 20 seconds. Is 28 V LED steady GREEN on regulator?
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