C.E. Niehoff & Co. C505 Troubleshooting Guides - Manual (Page 7)

Page 7 TG70C
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 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)
Temperature-Voltage Sense/J1939 Harness Troubleshooting
To verify temperature sense function on T-VS/J1939 harness:
1. With master battery switch on, key on, engine on, and loads off, apply a warm air source (such as a hair dryer, not to
heat above 120°F) to battery negative terminal of harness. Charge voltage should decrease as temperature increases.
If charge voltage increases or shows no change as temperature increases, go to step 2.
2. If charge voltage increases or shows no change as temperature increases from step 1:
a. With master battery switch on, key off, and engine off, check for battery voltage across pin E in 5-pin connector
(pin J in 10-pin connector) on T-VS/J1939 harness and ground with meter in VDC scale. If no battery voltage exists,
entire harness is defective and must be replaced. If battery voltage exists, go to step 2b.
b. With master battery switch on, key off, and engine off, check for a resistance reading of 5-15K Ohms at 70ºF (20ºC)
across pin B in 5-pin connector (pin H in 10-pin connector) on T-VS/J1939 harness and ground with meter in K
Ohm scale. (Note: If ambient temperature is higher, resistance will measure less than listed and vice versa.) If test
fails, see CEN Service Bulletin SB27. If test passes, go to chart on page 8.