Section 06: ELECTRICAL
PA1562
21
8. A constant drain caused by a shorted circuit
such as an exposed wire or water infiltration
in junction boxes causing ground fault.
9. Extended operation of preheating system
with engine not running.
10. Failing to close disconnect switches during
the night.
3.9 TROUBLESHOOTING
If a battery is known to be good and then has
not performed satisfactorily in service for no
apparent reason, the following factors may
reveal the cause of trouble:
1. Vehicle accessories and disconnect
switches inadvertently left on overnight.
2. Defects in the charging system, such as
high wiring resistance, faulty alternator,
regulator or battery equalizer.
3. A vehicle electrical load exceeding the
alternator (or battery equalizer) capacity,
with the addition of electrical devices, such
as CB radio equipment, a cellular phone or
additional lighting systems.
4. Defects in the electrical system, such as
shorted or pinched wires.
5. Extended driving at a slow speed while
using many accessories.
6. Loose or poor battery cable-to-post
connections, previous improper charging of
a run-down battery, or loose hold-down
clamp bolts.
7. High-resistance connections or defects in
the cranking system.
3.10 "BAT" BATTERY VOLTAGE INCORRECT
TELLTALE LIGHT
If the “BAT" (battery voltage incorrect) telltale
light is illuminated, check the 24-volt voltmeter to
determine if the battery voltage is too high or too
low.
NOTE
According to the battery charging condition, it
is normal that "BAT" telltale light illuminates
upon starting the engine and stays illuminated
for a few seconds. This is caused by the
normal voltage drop of the battery during
starting.
3.10.1 "Bat" Telltale Light Definitions
Voltmeter drops below 24.4 volts dc
Check alternator output.
Check voltage regulator.
Check battery connections.
Check battery cells.
o Check battery equalizer connections.
Voltmeter exceeds 30 volts dc
o Check alternator output.
o Check voltage regulator.
o Check battery connections.
Battery Balance
NOTE
Allow at least 15 minutes to balance batteries
after any corrective measure has been taken.
1. Batteries out of balance (difference greater
than 1.5 volts between the two battery
banks).
o Check battery equalizer connections.
o Check equalizer cables for proper gauge.
o Check battery connections.
2. Demand for 12-volt power exceeding rated
amperage output of battery equalizers
causing batteries to go out of balance.
o Reduce 12-volt load or install additional
battery equalizer(s).
4. TROUBLESHOOTING AND TESTING THE
MULTIPLEX VEHICLES
4.1 ELECTRICAL SYSTEM DIAGNOSTIC
Using the message center display (MCD), check
if there are active errors in the vehicle electrical
system. With the SYSTEM DIAGNOSTIC menu,
highlight FAULT DIAGNOSTIC and then
highlight ELECTRICAL SYSTEM to request a
diagnostic of the electrical system from the
CECM. Press the enter key. If applicable, the
MCD shows the multiplex device ID, the fault
messages or fault codes recorded. When more
than one fault is recorded, an arrow pointing
down appears on the right of the display. Use
the down arrow to see all the fault messages.
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