Jeep 1996 Grand Cherokee Service Manual page 264

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GENERAL INFORMATION
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
DESCRIPTION AND OPERATION
BATTERY TEMPERATURE SENSOR . . . . . . . . . . 2
CHARGING SYSTEM OPERATION . . . . . . . . . . . 1
GENERATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
VOLTAGE REGULATOR . . . . . . . . . . . . . . . . . . . . 2
DIAGNOSIS AND TESTING
BATTERY TEMPERATURE SENSOR . . . . . . . . . . 6
CHARGING SYSTEM RESISTANCE TESTS . . . . . 3
GENERAL INFORMATION
OVERVIEW
The battery, starting, and charging systems oper-
ate with one another, and must be tested as a com-
plete system. In order for the vehicle to start and
charge properly, all of the components involved in
these systems must perform within specifications.
Group 8A covers the battery, Group 8B covers the start-
ing system, and Group 8C covers the charging system.
Refer to Group 8W - Wiring Diagrams for complete circuit
descriptions and diagrams. We have separated these sys-
tems to make it easier to locate the information you are
seeking within this Service Manual. However, when
attempting to diagnose any of these systems, it is impor-
tant that you keep their interdependency in mind.
The diagnostic procedures used in these groups
include the most basic conventional diagnostic meth-
ods to the more sophisticated On-Board Diagnostics
(OBD) built into the Powertrain Control Module
(PCM). Use of a induction milliampere ammeter, volt/
ohmmeter, battery charger, carbon pile rheostat (load
tester), and 12-volt test lamp may be required.
All OBD-sensed systems are monitored by the
PCM. Each monitored circuit is assigned a Diagnos-
tic Trouble Code (DTC). The PCM will store a DTC in
electronic memory for any failure it detects. See the
On-Board Diagnostics Test in Group 8C - Charging
System for more information.
DESCRIPTION AND OPERATION
CHARGING SYSTEM OPERATION
The charging system consists of:
• Generator
CHARGING SYSTEM
CONTENTS
page
CHARGING SYSTEM . . . . . . . . . . . . . . . . . . . . . . 2
CURRENT OUTPUT TEST . . . . . . . . . . . . . . . . . . 5
ON-BOARD DIAGNOSTIC SYSTEM TEST . . . . . . 6
REMOVAL AND INSTALLATION
BATTERY TEMPERATURE SENSOR . . . . . . . . . . 8
GENERATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
SPECIFICATIONS
GENERATOR RATINGS . . . . . . . . . . . . . . . . . . . . 8
TORQUE SPECIFICATIONS . . . . . . . . . . . . . . . . . 8
• Electronic Voltage Regulator (EVR) circuitry
within the Powertrain Control Module (PCM)
• Ignition switch (refer to Group 8D, Ignition Sys-
tem for information)
• Battery (refer to Group 8A, Battery for informa-
tion)
• Battery temperature sensor
• Voltmeter (refer to Group 8E, Instrument Panel
and Gauges for information)
• Wiring harness and connections (refer to Group
8W, Wiring for information)
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.
The amount of DC current produced by the gener-
ator is controlled by the EVR (field control) circuitry,
contained within the PCM. This circuitry is con-
nected in series with the second rotor field terminal
and ground.
A battery temperature sensor located in the bat-
tery tray housing, is used to sense battery tempera-
ture. This temperature data, along with data from
monitored line voltage, is used by the PCM to vary
the battery charging rate. This is done by cycling the
ground path to control the strength of the rotor mag-
netic field. The PCM then compensates and regulates
generator current output accordingly.
All vehicles are equipped with On-Board Diagnos-
tics (OBD). All OBD-sensed systems, including the
EVR (field control) circuitry, are monitored by the
PCM. Each monitored circuit is assigned a Diagnos-
tic Trouble Code (DTC). The PCM will store a DTC in
CHARGING SYSTEM 8C - 1
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