Dodge RAM TRUCK 1500 1995 Service Manual page 343

8A -10 BATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICS
I G N I T I O N O F F
DRAW
GENERAL INFORMATION
Ignition-Off Draw (10D) refers to power being
drained from the battery with the ignition switch
turned OFF. A normal vehicle electrical system will
draw from 5 to 20 milliamps (0.005 - 0.020 amps).
This is with the ignition switch in the OFF position,
and all non-ignition controlled circuits in proper
working order. The 20 milliamps are needed to sup­
ply PCM memory, digital clock memory, and electron­
ically-tuned radio memory.
A vehicle that has not been operated for approxi­
mately 20 days, may discharge the battery to an in­
adequate level. When a vehicle will not be used for
20 days or more (stored), remove the IOD fuse in the
Power Distribution Center (PDC). This will reduce
battery discharging.
Excessive battery drain can be caused by:
• electrical items left on
• faulty or improperly adjusted switches
• internally shorted generator
• intermittent shorts in the wiring.
If the IOD is over 20 milliamps, the problem must
be found and corrected before replacing a battery. In
most cases, the battery can be charged and returned
to service. .
DIAeiOSiS
Testing for high-amperage IOD must be per­
formed first to prevent damage to most milli-
amp meters.
When testing a diesel engine-equipped vehicle
(dual batteries), do not check IOD between bat­
teries. One battery may be at a higher state-of-
charge than the other, which will cause a high
IOD between the batteries only. Remove nega­
tive cable from passenger side battery negative
post prior to performing the IOD diagnosis out­
lined below.
(1) Verify that all electrical accessories are off.
Turn off all lamps, remove ignition key, and close all
doors. If the vehicle is equipped with illuminated en­
try or electronically-tuned radio, allow the systems to
automatically shut off (time out). This may take up
to 3 minutes.
(2) Determine that the underhood lamp is operat­
ing properly, then disconnect or remove bulb.
(3) Disconnect negative cable from battery.
(4) Connect a typical 12-volt test lamp (low-watt­
age bulb) between the negative cable clamp and the
battery negative terminal. Make sure that the doors
remain closed so that illuminated entry is not acti­
vated.
The test lamp may light brightly for up to 3 min­
utes, or may not light at all, depending upon the ve­
hicle's electrical equipment. The term brightly, as
used throughout the following tests, implies the
brightness of the test lamp will be * the same as if it
were connected across the battery.
The test lamp must be securely clamped to the neg­
ative cable clamp and battery negative terminal. If
the test lamp becomes disconnected during any part
of the IOD test, the electronic timer function will be
activated and all tests must be repeated.
(5) After 3 minutes the test lamp should turn off
or be dimly lit, depending upon the vehicle's electri­
cal equipment. If the test lamp remains brightly lit,
do not disconnect it. Remove each fuse or circuit
breaker (refer to Group 8W - Wiring Diagrams) until
test lamp is either off or dimly lit. This will isolate
each circuit and identify the source of the high-am­
perage draw.
If the test lamp is still brightly lit after disconnect­
ing each fuse and circuit breaker, disconnect the wir­
ing harness from the generator. If test lamp now
turns off or is dimly lit, see Charging System in this
group to diagnose faulty generator. Do not disconnect
the test lamp.
After high-amperage IOD has been corrected, low-
amperage IOD may be checked. It is now safe to in­
stall a milliamp meter to check for low- amperage
IOD.
(6) With test lamp still connected securely, clamp a
milliamp meter between battery negative terminal
and negative cable clamp.
Do not open any doors or turn on any electri­
cal accessories with the test lamp disconnected
or the milliamp meter may be damaged.
(7) Disconnect test lamp. Observe milliamp meter.
The current draw should not exceed 0.020 amp. If
draw exceeds 20 milliamps, isolate each circuit by re­
moving circuit breakers and fuses. The milliamp
meter reading will drop when the source of the draw
is disconnected. Repair this circuit as necessary,
whether a wiring short, incorrect switch adjustment
or a component failure is found.