Dodge RAM TRUCK 1500 1995 Service Manual page 351

8A -18 BATTERY/STARTING/CHARGING SYSTEMS DIAGNOSTICS
C H A R G I N G S Y S T E M
GENERAL INFORMATION
The charging system consists of:
• generator
@ voltage regulator circuitry (within PCM)
• ignition switch
• battery
• voltmeter
• wiring harness and connections.
Following is a general description of the major
charging system components. Refer to Group 8 W -
Wiring Diagrams for complete circuit descriptions
and diagrams.
The charging system is turned on and off with the
ignition switch. When the ignition switch is turned to
the ON position, battery voltage is applied to the
generator rotor through one of the two field termi­
nals to produce a magnetic field. The generator is
driven by the engine through a serpentine belt and
pulley arrangement.
As the energized rotor begins to rotate within the
generator, the spinning magnetic field induces a cur­
rent into the windings of the stator coil. Once the
generator begins producing sufficient current, it also
provides the current needed to energize the rotor.
The wye (Y) type stator winding connections de­
liver the induced AC current to 3 positive and 3 neg­
ative diodes for rectification. From the diodes,
rectified DC current is delivered to the vehicle elec­
trical system through the generator battery and
ground terminals.
The amount of DC current produced by the gener­
ator is controlled by the generator voltage regulator
(field control) circuitry, contained within the Power-
train Control Module (PCM)(Fig. 21). This circuitry is
connected in series with the second rotor field termi­
nal and ground.
Voltage is regulated by cycling the ground path to
control the strength of the rotor magnetic field. The
generator voltage regulator circuitry monitors system
line voltage and ambient temperature. It then com­
pensates and regulates generator current output ac­
cordingly.
The generator is serviced only as a complete as­
sembly. If the generator fails for any reason, the en­
tire assembly must be replaced. The generator
voltage regulator (field control) circuitry can be ser­
viced only by replacing the entire PCM.
All vehicles are equipped with On-Board Diagnos­
tics (OBD). All OBD-sensed systems, including the
generator voltage regulator (field control) circuitry,
are monitored by the PCM. Each monitored circuit is
assigned a Diagnostic Trouble Code (DTC). The PCM
will store a DTC in electronic memory for any failure
it detects. See Using On-Board Diagnostic System in
this group for more information.
Fig. 21 Charging System Components - Typical
DIAGNOSIS
When the ignition switch is turned to the ON posi­
tion, battery potential will register on the voltmeter.
During engine cranking a lower voltage will appear
on the meter. With the engine running, a voltage
reading higher than the first reading (ignition in ON)
should register.
The following procedures may be used to diagnose
the charging system if:
• the voltmeter does not operate properly
• an undercharged or overcharged battery condition
occurs.
Remember that an undercharged battery is often
caused by:
• accessories being left on with the engine not run­
ning
• a faulty or improperly adjusted switch that allows
a lamp to stay on (see Ignition-Off Draw in this
group).
INSPECTION
(1) Inspect condition of battery cable terminals,
battery posts, connections at engine block, starter so­
lenoid and relay. They should be clean and tight. Re­
pair as required.