C.E. Niehoff & Co. C703/C703A & C706 Troubleshooting Guides - Manual (Page 6)

Page 6 TG31K
OVCO Troubleshooting
Shut down vehicle and restart engine. If alternator functions normally after restart, a “no output condition” was normal
response of voltage regulator to “high voltage” condition. Inspect condition of electrical system, including loose battery
cables, both positive and negative. If battery disconnects from system, it could cause “high voltage” condition in electrical
system, causing OVCO circuit to trip.
If you have reset alternator once, and electrical system returns to normal charge voltage condition, there may have been
a one time, high voltage spike, causing OVCO circuit to trip.
If OVCO circuit repeats cutout a second time in short succession and shuts off alternator field circuit, try third restart.
If OVCO circuit repeats cutout, check that pin F in alternator-to-regulator harness is not shorted to B+ terminal on
alternator and that pin A in alternator-to-regulator harness is not shorted to B–. If it is shorted, alternator is defective.
If not, regulator is defective.
Section C: On-Vehicle Troubleshooting
(CONT’D)
A2-341 Regulator Troubleshooting
Main diagnostic feature is a tricolored LED located on the front of the regulator. LED works like a voltmeter, measuring
charging voltage. See Table 2 for LED diagnostics.
This regulator has OVCO (overvoltage cutout) that will trip at vehicle electrical system voltage above 33 volts that exists
longer than 3 seconds. OVCO feature detects high voltage and reacts by signaling relay in alternator field circuit to open.
This turns off alternator (LED is flashing RED). OVCO circuit is reset when engine is restarted or can also reset when
system voltage normalizes after 2-minute wait.
An additional temperature-voltage sense/J1939 harness may or may not be used with the A2-341 regulator:
• When optional temperature-voltage sense/J1939 harness is not connected, regulator will operate in fixed voltage
setting determined by the select switch position on the bottom of the regulator.
• When optional temperature-voltage sense/J1939 harness is connected, regulator will automatically optimize the
charge voltage for battery type selected based on temperature. Also, vehicle manufacturer-requested functions of
J1939 interface are available through connector.
LED COLOR STATUS
TABLE 2 — A2-341 Regulator LED Diagnostics with Engine On*
Alternator and regulator operating normally. GREEN Solid
Low system voltage — Electrical load exceeds
alternator rating at present rotor speed.
ACTION
No action required.
When loads decrease or speed increases, LED
should be solid GREEN. If not, check drive belt and
charging system connections.
Replace alternator.*
AMBER Solid
High system voltage – May occur during
normal load switching.
Indicates voltage above setpoint but below OVCO
threshold (less than 33 volts).
Indicates voltage exceeds 33 V for more than
3 seconds. System diagnosis required. See “OVCO
Troubleshooting” section below.
RED Solid
Alternator fault — No output.* Flashing*
Flashing OVCO tripped.
No power to ignition or regulator is defective. OFF Go to Chart on page 7.
* LED will flash AMBER for one minute upon start-up/shutdown—if regulator does not sense alternator rotation, regulator will time out.
Temperature-Voltage Sense/J1939 Harness Troubleshooting
To verify temperature sense function on T-VS/J1939 harness: Apply a warm air source (such as a hair dryer, not to heat
above 120°F) to battery negative terminal of harness. B+ battery voltage should decrease as temperature increases.
If voltage does not decrease: Check for a resistance reading of 5-15K Ohms across pin H in 10-pin connector on T-VS/
J1939 harness and ground with meter in K Ohm scale. Then check for battery voltage across pin J on T-VS/J1939
harness and ground with meter in VDC scale. If both readings pass, go to chart on page 7. If one or both readings fail,
verify proper terminal connections on B+ and B− terminal leads from T-VS/J1939 harness. If both terminal connections
are good, entire harness is defective and should be replaced.